Hmm... I do a decent job at new, exploratory library code with a glass of wine. Not business logic, not exacting data invariants, nothing I would ever ship to production, but exploring interfaces for a library? Yeah. Asking "What does this really need to do? How do I really wish that I could write the calling/collaborating code?"

I wouldn't trust logic I wrote with alcohol in my system, or any tests that I wrote with alcohol, but getting at the heart of "Why does this library need to exist? What should it actually allow?" is enhanced a tiny bit by a mildly-altered mental state.

Over time, I've decided that it is because I get chatty with wine, and designing a library interface feels like a conversation between me and future engineers who might use said library. And then I stash it away to read and reconsider while sober.