Most of the time it's my fault. But my husband has selective hearing. So when my computer is dying and I say "I don't care about anything except the quilting directory" he saves everything except the quilting directory... Or when we were getting ready for a visit from his mom, I told him I didn't want the rejected blocks from my cat block swap to go to the storage unit. I wasn't alarmed at first that I couldn't find them, I wanted to use them in the back of the quilt. But time went on. And on. And finally I finished the top and so immediately after finishing it we closed out the storage locker and guess where that stack of blocks was?
So that's the trick. Make a replacement block and then turn around and the missing one will fall on your head.