After I read this Lifehacker article on boosting morale with inbox fuzzies, I was reminded of how important it is to keep up your self-esteem by making happy and motivating things visible in your daily life.
One example is the gym streak board I started. I've also found myself re-reading emails where people say nice things about me. It's always a huge boost to know that Person A thinks I'm awesome. So I marked those emails with a "yay_me" label in Gmail. I'll have to keep thinking of more ways to make happy stuff prominent in my life.
This discussion of nice emails reminds me of a particular incident. I have one physicist friend who's always a bit reserved. That's his personality. I went up to his office and waited for him to finish his email so we could go out to lunch. Glancing over his shoulder, I noticed an email I had written to my physics colleagues months ago about some personal problems I was having. Now this occurrence was not because he neglected to clear out his email. There were only about a dozen emails in the inbox. It was nice to know that he kept that email there because he cared about how I was doing.