When I drank, the usual evening went: "I haven't had enough to drink yet. My playing and singing will get better when I have hit the 'optimum' level", to, "All right! I'm in the groove now!". to, "I'm too drunk to play worth a shit. Guess I'll just give up and drink."
Now that I don't drink anymore, I'm always at my "optimum" level. That's not to say that I always play well. But, if I suck I know that it's just me having a bad night, not that the chemicals are out of balance. And it's not "Puritanism". It's "sanity".