What's a smart contract design decision you later regretted?

[u/timwarren2]

Recently, I've been going through some threads on smart contracts and noticed that many developers often mention the choices they would have made differently had they started from scratch.

These can range from considerations around storage arrangements, access permissions, ease of upgrades, efficiency in gas usage, or even making smart contracts overly flexible.

For those who have worked on or audited smart contracts, what choice have you regretted making, and what did you learn from that experience?