What’s your “ignorance debt” as a business owner?

I’ve been thinking a lot about the idea of “ignorance debt”, the stuff you didn’t know when you started your business that later came back to bite you (or cost you time/money/energy).

For example, mine was not understanding how inventory forecasting actually works. I used to restock based on gut feeling, and it caused either overstock or missed sales every single time. It wasn’t until I started tracking actual weekly demand and lead times that I realized how much money I had left on the table.

Curious, what was your ignorance debt?

Something you wish you had learned earlier, or something you ignored until it became too expensive not to fix?