If some part of the software has problems, runs slow or has bugs but nobody is complaining, then there's no problem.
This depends very much on context. To pick an extreme example, if you're writing the control software for a nuclear weapon and you know you have a bug that might cause it to activate unintentionally if you eat a banana while it's raining outside, I think we can reasonably agree that this is still a problem even if so far you have always chosen an apple for lunch on wet days.
This is bad advice. It's like saying "go into a bar and start picking up fights".
If some part of the software has problems, runs slow or has bugs but nobody is complaining, then there's no problem. Why waste time improving it?
Almost 100% of the time when you solve a problem you just create new problems of different kind in turn.
Be lazy. The less code you write the better off you are.