Your head can only hold so much. Even very simple problems can flood your mind and escape your ability to follow them if they carry on long enough. For example addition is quite simple but if you are asked to keep a running sum for hours upon hours you are likely to begin making mistakes at some point.
Programmers face similar problems with software. Many seemingly simple things can be made unnecessarily complex by allowing a block to run-on without bound. The non-technical analogy might run something like this:
Which response to a query is preferable?
It is most assuredly true.