Dealing with other people's perceptions. When I start a new job, everyone sizes me up and forms impressions about my skill or 'level' or whatever. What impressions? How do they form them? Do they actually have anything to do with me? Typically, at first everyone assumes I'm an idiot. Then, after I've tackled something hard that impresses people, they upgrade to "not a total idiot, but probably green/ignorant". Then slowly over time, as I solve a large variety of problems with decent, well-performing, and not-so-buggy code, they upgrade me to "pretty smart, actually!" Eventually I'm the senior guy. Now, begin a new job and start at the beginning again. Even with 20 years experience and a long list of successful shipped products, I still start every new job with the presumption, "probably an idiot."