"The gist is that it’s tough to get unbiased feedback during customer validation." - I wish this was taught along with lean startup content. Too many times I have heard founders say they validated the idea when all they have done is gotten biased feedback while asking self-fulfilling questions.
I say it every time, to every founding team I meet. Read “The Mum Test”[1]. It will make you aware that you to get unbiased feedback you need to remove your identity from the idea so that people aren’t nice to protect you. [1] http://momtestbook.com/
Basically, if you want to find out whether you're baby's ugly, you have to make sure people think the photos are of a baby, not your baby.