The sting in the short term definitely sucks, but the time wasn't wasted. Now you know what you're doing, so putting it back together should go by much faster than putting it together the first time. Similar things have happened to me before, where something will happen and I'll lose a big chunk of writing, or I'll forget to hit the record button before taking on a tough boss challenge. Even though I lose the progress I made, it's not like I lost the experience. I know what made the scene work the first time, or I know what strategy brought me to victory. The knowledge accumulated from the first attempt is still there, and it'll help you make up for lost time.