There is no substitute for testing. Use it under ludicrous conditions. Turn off your database server while you are saving an order. Unplug the keyboard. Launch 3 copies of Word.
Coders are notoriously bad testers.
The best testers are users, children, and monkeys in that order. It's natural for coders to try to defend their software. We want to have pride in what we do. So we think of all users as idiots and blame them when our software fails them. Remember that the goal of our code is to enable them.