The problem with "rules" is that they live in an ideal world, not the real world. "Give up only 15% of your company" sure, if you are the next Google, but even then every raise they did wasn't perfect. Let's be honest there is an ideal way you would build a company, but it doesn't exist for anybody. Startups are hard and messy. You do the best you can, but you can't just know in advance you're picking the best idea, the best people and fundraising quickly. It's not like that at all.