I use this a lot when interviewing at companies, but find it useful when interviewing senior folks: "What is a technical decision you made on this project that

I use this a lot when interviewing at companies, but find it useful when interviewing senior folks: "What is a technical decision you made on this project that you wish you would have made differently, that you are still living with today?" This opens up a lot of conversation around how it could have been solved better, what they know now that made it apparent is a sub-optimal decision, what steps were taken to minimize the impact once this fact was discovered, and is there any plan to correct in the future or just live with it. The big thing is to see that someone has not only built something, but maintained it after the fact, and for long enough to see the impact of trade-offs.