Some problems are easier than others to diagnose. For example, it’s clear what the cause (and the solution) is when you see an error such as Web application cannot write to /var/www/cache/. Unfortunately, such detailed output is rarely available because it may raise performance or security issues.
In many production environments, detailed logging that shows the result of every operation is too expensive, in terms of additional CPU and disk input/output operations. Nevertheless, checking the logs is the first step to follow once you realize that the solution to a problem is not obvious.