It is very rare that everything goes as planned during any event. Mishaps are an inevitable part of event management. Having put so much effort and time into planning, it is hard not to get upset, angry and emotional when it happens.
The key however, is to accept the issue at hand, and deal with it to remedy the problem as effectively and quickly as possible. Stay calm and assess the issue and carry on as the show must go on. The post-event review is when you can truly analyze what the problems were and evaluate what went wrong.