There’s a certain thrill in spilling a big secret. It can be satisfying, liberating, gratifying. This is the genesis of the PostSecret project, started by Frank Warren, which now encompasses an extensive media empire: the most-viewed blog on the Web at postsecret.com, a speaking tour on college campuses and, with the release of “A Lifetime of Secrets: A Postsecret Book,” four popular books from a major publishing house.

Warren’s idea was to ask the population at large to send him secrets written on postcards, decorated however the sender wants. He pulls the ones that speak to him, and they get put on the blog, in a book or on the traveling exhibit. As the de facto editor of the secrets, Warren doesn’t select for any certain type: some are happy, some are humorous, some are non-sequiturs and some are devastating. Some tell a personal, specific anecdote, but it is often the simplest (such as “I love her” or “I married the wrong man”) that are the most penetrating.

There’s been a lot of debate about art and ownership regarding the PostSecret project. While the written secrets are obviously the focus of the project, the decorations and artistry really do add something to it — the impact of the secrets would not be the same without it. The secrets become intimately tied up in the art; the same words with two different visuals will diverge in meaning. The question of ownership also remains: while the authors consent to their cards being published by sending them in, Warren, to his credit, presents them with absolutely no commentary, not imprinting his own ideas on them. The secret-bearers remain in firm ownership of their own secrets, and there is no intermediary between secret and reader.

Part of the popularity of PostSecret can be explained by its therapeutic effect on the reader. While it is interesting to read the secrets of anonymous others, it is compelling to read secrets that might be your own. This is the secret to PostSecret — your own secret, artfully done, in a pithy phrase that you yourself could never articulate.

This fourth PostSecret volume, like all the others, is a collection of these postcards, maybe 400 in all. “A Lifetime of Secrets,” however, approaches the secrets a little differently, in that they are arranged chronologically, approximating the stages in one’s life. While the previous books were arranged thematically, if at all, this book is the first attempt to present a real narrative — literally, a lifetime of secrets. So “When I was in kindergarten I thought the overhead in our classroom was an x-ray machine” is at the beginning, and “I will die alone and happy” is at the end. Most of the cards, though, do not have any particular age signifier, which keeps the book from reading like a catalogue of age-specific fears.

Warren’s decision to sort the cards roughly by age is welcome because, as one might expect, the majority of the cards on any given week’s posting seem to be from people between the ages of 15 and 25 — the Angst Years, if you will. It’s refreshing to see secrets from the older end of the spectrum, although they tend to be the most morbid and depressing; the specter of death hangs over most of them, such as “I have been planning my husband’s funeral for 24 years” and, painfully, “I am scared...to die with regrets.”

PostSecret has become a social phenomenon in just a few short years, one so expansive that 70-year-old people terrified of death are sending in secrets. “A Lifetime of Secrets” is just another step in the expansion of the project. At this point, it’s not even necessary to send in your secret. Chances are, it’s already there.