I've been in the industry for 35 years now (and hacking computers before that). If I picked just one accomplishment, I'd have to choose just one from all the accomplishments that I'm equally proud of. Furthermore, if I chose one from earlier in my career, one which was really neat and a lot of fun and technically sweet and saved the project's bacon, you might think I'd not done much interesting stuff since then.

If you ask this, you're not going to get much actual data. You won't see me write code, you won't see me react to something totally new.

I might ask this during a screening interview, but it's a soft question that should lead into more concrete technical assessments.

So: Meh. No silver bullet.