I once stayed at work for 36 hours straight to finish assembling a batch of circuit boards for a customer's prototype. I dropped them off at FedEx for next day AM shipping right before they closed on a Saturday and felt pretty good to just barely make the deadline!!

Well Monday morning, the customer assembles the first prototype and it lights on fire. Turns out there were lots of other problems and all my work was for nothing.

I learned a lot from the experience!