Being a drunk is always a good excuse for failure, I find.
Failing whilst sober simply means you're a run-of-the-mill incompetent, nothing to write home about, just like everyone else.
But if you're drunk when disaster strikes or you fuck up monumentally, it's totally acceptable to blame the booze.
After a while nobody expects very much of a drunk at all. People are amazed if you get up in the morning. I've just turned 40, and already I've developed something of a drinker's blush. Just like dad's. I've given up wine and am sticking to beer.
I count the units and stay away from the pubs.