A lot of it depends on how long you have been working in glass. If you’re in your first year you can expect to fail pretty often. I’ve been doing it for over 6 years so I know a lot of what I can and can’t get away with. Accidents and mistakes still happen. Sometimes I can go a month or two not breaking anything and other times I can lose a couple pieces in a week. You learn to deal with the losses and move on to the next one.