Why do certain bugs take longer than others to be fixed?

Some things are just that much harder to track down, especially when dealing with code structures as elaborate and complex as the ones we implement. Some issues are easy to spot and can be remedied within minutes of being notified of them, while some of the more complex ones require a bit more time. In some cases there are quick fixes that could be made, but those quick fixes then create their own problems which then need to be dealt with, and that's not really a fix at all is it?