During my study of happiness, I noticed something that surprised me: I often learn more from one person's highly idiosyncratic experiences than I do from sources that detail universal principles or cite up-to-date studies.

Putting myself into categories is fun, and I think it also gives me insight into my own nature. When I see myself more clearly, I can more easily see ways that I might do things differently, to make myself happier. Categories can be unhelpful, however, when they become too all-defining, or when they become an excuse.

I love taxonomies, categories, ways of dividing people into groups.

Remember that although the distinction can be difficult to draw, loneliness and solitude are different.

I have a terrible memory of my own past. I can barely remember my childhood. I have few memories from college and law school - though once I got married, I got the advantage of being able to consult my husband's memory.

Habit allows us to go from 'before' to 'after,' to make life easier and better. Habit is notorious - and rightly so - for its ability to direct our actions, even against our will; but by mindfully shaping our habits, we can harness the power of mindlessness as a sweeping force for serenity, energy, and growth.

Most decisions don't require extensive research.

Most people enjoy 'potato-chip news' from time to time - to track a presidential election or the Oscars. However, some are particularly drawn to material that makes them feel shocked, frightened, insecure, or indignant, and that's what potato-chip news often provides.

Growing up in Kansas City, I was always neat, the teacher's pet, know-it-all type.

One thing I wish I could tell my younger self: take photos of everyday life, not special occasions; later, that's what will be interesting to you.

People often assume that the same approach will work for everyone, that the same habits will work for everyone, and that everyone has the same aptitude and appetite for forming habits, but from my observation, that's not true.

Sometimes, counter-intuitively, it's easier to make a major change than a minor change. When a habit is changing very gradually, we may lose interest, give way under stress, or dismiss the change as insignificant. There's an excitement and an energy that comes from a big transformation, and that helps to create a habit.

For one person, organized files might be a crucial tool for creativity; another person finds inspiration in random juxtapositions.

Kennedy was president for only 1,037 days, but during his short tenure, he achieved much. At the Cold War's most dangerous hour, he preserved the peace. He improved relations with the Soviet Union and replaced tension over Berlin with a limited test ban treaty.

We can use decision-making to choose the habits we want to form, use willpower to get the habit started, then - and this is the best part - we can allow the extraordinary power of habit to take over. At that point, we're free from the need to decide and the need to use willpower.

Whenever I'm trying to decide how to spend my precious time, energy, or money, I ask myself a series of questions. 'Will this broaden or deepen my relationships?' 'Will this contribute to an atmosphere of growth in my life?' 'Is this a way to 'Be Gretchen?' and 'Will this help connect me to my past?'

Like most people, I have several pet subjects - that may or may not be interesting to other people. Don't get me started on happiness, or habits, or children's literature, or Winston Churchill, unless you really want to talk about it.

Happiness is a critical factor for work, and work is a critical factor for happiness. In one of those life-isn't-fair results, it turns out that the happy outperform the less happy. Happy people work more hours each week - and they work more in their free time, too.

In 'Before and After,' I identify the sixteen strategies that we can use to make or break our habits. Some are quite familiar, such as 'Monitoring,' 'Scheduling,' and 'Convenience.' Some took me a lot of effort to identify, such as 'Thinking,' 'Identity,' and 'Clarity.'

It was my interest in happiness that led me to the subject of habits, and of course, the study of habits is really the study of happiness. Habits are the invisible architecture of everyday life, and a significant element of happiness.

Although we often assume that feelings inspire actions, in fact, actions also inspire feelings. By pushing myself to act happier, I make myself feel happier.

One of my key realizations about happiness, and a point oddly under-emphasized by positive psychologists, given its emphasis in popular culture, is that outer order contributes to inner calm. More than it should.

I collect axioms, paradoxes, maxims, teaching stories, proverbs, and aphorisms of all sorts, because I love to see complex ideas distilled into a few words.

Don't let yourself fall into 'empty.' Keep cash in the house. Keep gas in your tank. Keep an extra roll of toilet paper squirreled away. Keep your phone charged.

One of my most important 'Secrets of Adulthood': Outer order contributes to inner calm.

My writing tends to become very dense, so I have to keep some cushion. Sometimes, words that seem superfluous are actually essential for the overall effect.

It's so easy to use tired, shopworn figures of speech. I love using long, fancy words but have learned - mostly from writing my biography of Winston Churchill - that short, strong words work better. I am ever-vigilant against the passive and against jargon, both of which are so insidious.

Now, the term 'friend' is a little loose. People mock the 'friending' on social media, and say, 'Gosh, no one could have 300 friends!' Well, there are all kinds of friends. Those kinds of 'friends,' and work friends, and childhood friends, and dear friends, and neighborhood friends, and we-walk-our-dogs-at-the-same-time friends, etc.

It's easier to get rid of things when you're giving them to someone who can use them, but don't let this kind intention become a source of clutter itself. I have a friend who has multiple piles all over her house, each lovingly destined for a particular recipient.

Do I need fifty finger-painted pictures by my toddler, or is one enough to capture this time of life? Mementos work best when they're carefully chosen - and when they don't take up much room!

I'm always trying to figure out ways to keep hold of memories. My one-sentence journal, for instance.

Work done by other people sounds easy. How hard can it be to take care of a newborn who sleeps 20 hours a day? How hard can it be to keep track of your billable hours? To travel for one night for business? To get a 4-year-old ready for school? To return a few phone calls? To load the dishwasher? To fill out some forms?

Often, the more reliably you perform a task, the less likely it is for someone to notice that you're doing it and to feel grateful and to feel any impulse to help or to take a turn.

It's hard to avoid 'unconscious overclaiming.' In unconscious overclaiming, we unconsciously overestimate our contributions relative to others. This makes sense, because we're far more aware of what we do than what other people do. Also, we tend to do the work that we value.

I'm much calmer when there's no TV or music playing in the background.

I do better with routines and predictability. I don't react well when there's a sudden change in the schedule.

In 'Happier at Home,' I write a lot about my struggle to create an unhurried atmosphere at home.

For quotes, I have one document for general quotes; the other for happiness-related quotes, which I use for the 'Moment of Happiness,' my daily emails of happiness quotes.

For notes related to books I'm writing, I've wondered whether I should organize my notes better, but I do find that the action or scrolling through them and seeing odd juxtapositions of ideas helps to stimulate my own ideas and creativity. I worry that if I kept the notes in a highly-structured way, I might lose some of these benefits.

Watching TV is companionable: you share an experience, you can comment on the action here and there for a bit of conversation... it's a way of showing someone that you want his or her company and engaging in a low-key, pleasant, undemanding way.

An enormous amount of ingenuity and creativity goes into commercials, and they can be fascinating if you pay attention.

If you'd like to watch less television, try putting the remote away in a very inconvenient place and making yourself put it away every time you use it. If it's a big pain to turn on the TV and to change channels, you might find yourself drifting to other activities that will be more satisfying in the long run.

I always feel calmer when I exercise. In fact, that's probably the main reason I exercise.

Try to never say 'yes' on the phone; instead, say, 'I'll get back to you.' When you're actually speaking to someone, the desire to be accommodating is very strong, and can lead you to say 'yes' without enough consideration.

Take care of difficult calls or emails as quickly as possible. Procrastinating just makes it harder; getting them done gives a big boost of relieved energy.

When accepting a responsibility, imagine that it's something that you'll have to do next week. That way you don't agree to something just because it seems so far off that it doesn't seem onerous.

People are powerfully moved by imagination, belief, and knowledge. They can consider the past and future. They can make changes in their behavior out of reason in a way that animals can't do.

I really work on paying attention to the clues my self is giving myself. For instance, I think of myself in the third person. That allows me to manage myself better.

Children's literature is one of my joys, and it's also my mental comfort food.

Embrace good smells. No cost, no calories, no energy, no time - a quick hit of pleasure.