I'd love to be able to give you a citation for where this originated, but I have no idea. GoodReads attributes it to Socrates, which is basically never true. It's debated, but seems like it has religious origins.
Anyway, when it comes to those three questions, they don't all need to be answered with an enthusiastic yes. As a rule of thumb, you want 2 out of 3:
The last one's probably the most obvious, and hardest to argue against. But it's also the one that we do the least often. When was the last time you shared a kind truth with someone, just because you could?
The world is a hostile and competitve place. When we share honest and unprompted praise, compliments, or appreciation, the world gets slightly nicer. It's a long journey, and this is just one step, but it's one step towards a world I'd rather live in.
So take a moment to think to yourself. Think about the people that have helped you, the things you've read, the meetings you've enjoyed. Think about how people have helped make your life better, and repay the favour by thanking them.