Not financially.

I mean the decisions that seemed harmless at the time but created months of pain later.

Examples:

• Choosing a framework because it was trending.

• Skipping tests "just for the MVP."

• Building microservices before having users.

• Ignoring documentation because "everyone knows how it works."

• Naming a variable temp and starting a chain reaction of confusion.

Mine was optimizing a system before understanding the actual bottleneck. I spent weeks improving something that wasn't even the problem.

Looking back, the biggest engineering mistakes are rarely bugs. They're assumptions.

What's the technical decision you made that cost you the most time, stress, or sleep, even though it didn't directly cost money?

Bonus points if you would make the same mistake again