Sooner or later everybody makes a mistake. It is reasonable – we are only human. This doesn’t mean that your boss or your client will have understanding.
A few years ago I was working as a software developer for a company that was developing custom shopping cart for managing products manipulation for different branches in different countries. Each store had their own items and administrators could have copied parts (like description and images) from other stores. When I programmed this functionality I made an option which enables the administrator to choose from which and to which language they want to copy. It never occurred to me that they could forget to choose a language and I didn’t write a proper test. At one point, somebody did forget to select and chose to copy all images from one store to another. The system had a terrible flaw. It deleted all the images on the website. All 8.500.
When I realised what had happened I was in shock. That is when I learned a valuable lesson on how to act when you make a big mistake. Later on, as I was running my own business, I had a chance to deal with other peoples mistakes, and I managed to make a few more conclusions which I hope will help you when you make a big mistake at work.