What's One Piece of Advice You Wish You'd Ignored as a First-Time Founder? - I will not promote

We all get bombarded with advice when starting a company. Some of it's gold, but some of it's just plain wrong for your specific situation. What's one piece of advice you wish you had ignored? What well-intentioned guidance actually led you astray or wasted your time/resources? I will not promote. I'm hoping we can create a counter-guide of sorts, sharing the advice we should all be wary of.