I'm not sure if it is a result of getting older, change in diet and it doesn't really matter. I like a good wine, beer, whiskey or rum, but in the last six months I started notice that I don't sleep very well after drinking. I can have one or two beer or one glass of wine, but not much more. After that it starts to interfer with my sleep, costing me hours of sleep. Given the choice I'd always put a good nights sleep before a cozy evening with wine. I could just have the one drink, but to me at least, it's simply easier to just not drink at all.

If you're in a settings where you're almost expected to have a drink, you can just use my reasoning, that you don't sleep well after drink alcohol, it's honestly something most people seem to understand.

Small note on the: "just hating yourself when you fail" that's not productive. Recognize that you failed, that it's okay to fail, and examine why. Then start over and try to learn from you mistake. E.g. maybe don't have alcohol in the house, replace it with something else, for me its tea and sparkling water. (Having a replacement beverage for the time when I'd just relax and normally have a drink have helped a lot)