This reminds me of Jiro Dreams of Sushi, and his advice to his kids (paraphrased): I don't care what you do, as long as you do it every day for the rest of your life.
I think one of the main thing this advice misses is that if you're doing a "lean startup" then you could very well end up doing something different than what you started. It's hard to know what exactly the continuation will be in what you do.