Summoning that successful kind of creative, productive, free play state of mind is really difficult in software coding job interviews. There's a lot of back and forth, warming up as well as looking up things and experimenting to reach that flow state. Once you're in it, you know you're in it. You've shipped robust apps thanks to it.

Having to explain that almost instinctive process to a complete stranger who has control over your career and income can really hamper or destroy the ability to get into that groove. I've found it really useful to know about flow, what can get it going and when it's just not happening, and most interviews just aren't set up to encourage it. Csikszentmihalyi wrote a shorter book called "Finding Flow" which speaks of creating situations that bring out the best in others and us.