I don't know what it is about the number 3, but somehow, it's doable. It's not too much, but it's a start.
I don't know if you know this about me, but I am easily overwhelmed. And being overwhelmed causes me to shut down and seek escape. Let's face it: there are waaaaay more than 3 things each day in the world that deserve my attention. And since we're being perfectly honest here, there is absolutely no way I will ever accomplish all of those things in one day. Overwhelming.
But, I can choose the three that I wish to work on today, each day. That, I can do. Three things.
Anything else is gravy.