Make Your Bed: Little Things That Can Change Your Life...And Maybe the World by William McRaven was a very short (about an hour to read) book from the retired U.S. Navy Admiral and written out of a 2014 commencement speech on ten principles he learned in Navy Seal training...
2. You can't go it alone.
3. Only the size of your heart matters.
4. Life's not fair - drive on.
5. Failure can make you stronger.
6. You must dare greatly.
7. Stand up to the bullies.
8. Rise to the occasion.
9. Give people hope.
10. Never, ever quit.
The principles that resonated with me the most were the first, fourth, and tenth, with the tenth a fairly obvious one as to why it's important and first about starting your day with an accomplishment, something that can be built upon or even if nothing else goes right, something that got done out of the day.
The fourth principle about life not being fair was memorable with it's mention of how Navy drill instructors in San Diego would have people run from the beach to the water and get soaked, then roll in sand, and spend the rest of their training day as a "sugar cookie," caked in sand and extremely uncomfortable. What's key is that this directive was done sometimes as punishment for a mistake, and sometimes just because, to teach the valuable lesson that life's not always fair, you have to accept that and continue moving forward. Even if nothing else was of value from the book, this idea alone an important one.