“Yesterday it still worked and now it doesn't anymore, what did happen?"
"Why does it work on this computer and not on another one?"
I bet you have heard this before from your colleagues or may be you have yelled like this. :)
Anyway read this nice document from Hans De Smaele and try to reduce no of times you will hear this. But I’m death sure it wouldn’t be eliminated. :)
http://www.microsoft.com/belux/msdn/nl/community/articles/feb05_applicationdebugging.mspx