More than 30 years ago, my doctoral advisor handed me two envelopes. They contained identical copies of her recommendation letter for my faculty job applications.  And that day, she surprised me. As she handed me the letters, she said, "One is for your application file. Keep the other for your own file." I must have given her a quizzical look because she added, "In my top desk drawer, I keep a file of things--good reviews of my work, recommendation letters, notes from students. When I'm having a rotten day or doubting myself, I pull that file out to remind me that I do good work and make a difference."

[i] Mind you, I don't remember her exact words, but this is the gist of my takeaway from the conversation.