​What financial mistake looked harmless at first but ended up costing you the most?

One thing I’ve learned is that the biggest financial problems in a business usually aren’t the obvious ones. Most owners watch revenue closely, but things like poor cash flow management, slow-paying customers, unnecessary expenses, overhiring, underpricing, and inventory sitting too long can quietly eat away at profits. In my experience, some of the most expensive mistakes don’t feel expensive when you’re making them. They only become obvious months later when you look back and realize how much they cost.

I’m curious what financial lesson or mistake had the biggest impact on your business and what you learned from it.