Wisdom
I don't remember when I first came across this quote but lately I've been thinking about it a lot:
Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it? - Brian Kernighan, The Elements of Programming Style
The more I think about this the more I also think that I've gone about almost everything I've set out to do in my life, all wrong.