This lecture is from YCombinator and may be a bit self serving. I would take it with a grain of salt. I have noticed that YCombinator prefers multiple cofounders, and in this video they are now saying the cofounders all need to have the same amount of stock regardless of how much work you have put in in the past. That's very surprising advice. You may have slogged for a couple of years before taking on a cofounder, and you should both have the same amount of shares? This is not in your interest, but may be in YCombinator's: if they need to separate you from your company it is easier this way.