Things that I've learned as being a tech entrepreneur and as a software engineer is that it's super important to know to say "No" to things, more specifically choose which things to decide not doing. It comes in mind even when trying to tell the difference between a Junior Engineer and as Senior one, the ability and the skill to know what NOT to do. Telling from experience of more than 13 years as a software engineer, more than 5 years of running developer communities and over 3 years as an entrepreneur, I'll mention all the mistakes a long the way, trust me, it's not a success story :)