This is from "The Humble Programmer" of which I was reminded too. I think the term humility captures the essence of what the author is saying better than "lack

This is from "The Humble Programmer" of which I was reminded too. I think the term humility captures the essence of what the author is saying better than "lack of confidence". You can be confident in what you know, all while humbly accepting that there's a lot you don't know (and even more you don't know you don't know).