[noswi]

For me, it was a book on stoicism ("A Guide to the Good Life — The Ancient Art of Stoic Joy" by William B Irvine) that showed me that, while it's not possible to avoid the inevitable pains and losses — just semi-regular thoughts about it, imagining the world where the losses have already happened, allows immense enjoyment and appreciation of the current moments.

Also, as an unexpected bonus, the book showed that philosophy shouldn't neccesarily be only theoretical high-brow word games, it can be a pleasant and highly practical experience as well.