Biggest moment I had was when I was brewing 3 batches on consecutive days for a wedding. I had all the grain bills and hops laid out in bags and was on my first brew. After the first hop addition, I was going to start milling the 2nd and noticed torrified wheat amongst the grains. Its a pretty distinctive looking grain and I thought to myself, tomorrows brew doesn't have torrified wheat...OH F&&K. I was brewing the wrong beer entirely! Luckily, it was just an American Wheat vs a Pale Ale, so the mash routine was pretty similar and I had only done the bittering hops addition. I scrambled and got myself back together and was able to salvage the brew. Luckily, no one noticed at the wedding, and both beers were gone quickly. I never told the bride and groom that I messed up my beers they requested...