Reminds me of a passage from Philip Greenspun's article, How to Become as Rich as Bill Gates, http://philip.greenspun.com/bg/ : When I arrived at MIT as a first-year graduate student in electrical engineering and computer science, I asked a professor for help with a research problem. He said "The reason that you've having trouble is that you don't know anything and you're not working very hard." A friend of mine was…
When I was learning to kiteboard I was out one day for a couple hours, had a good session and decided I was ready to get out of the water. I wasn't exhausted, but I was getting tired.
My instructor came speeding up next to me and asked me what I was doing. I explained I was getting tired and wanted to head in. He tossed his really nice new kiteboard my way, told me to give him the old beat up kiteboard I was riding and to go back out. I was reluctant but he pushed me and I caved in. My session went from good to great, and I think my kiteboarding skills improved more in that extra hour than in many of the days prior.
Later that night I was telling my instructor how well I did on the newer board and how I had been ready to give up for the day. He told me "Sometimes you just have to push yourself that extra 5%, even when you think you can't." That statement has been a guiding principle throughout my life ever since.
Any time I feel like I'm in too much in my comfort zone, not challenging myself to learn new things, or feel I'm incapable of doing something, I remember my kiteboarder's adage and try to push myself just a little bit more. So far it seems to have worked well.