Here are a few software development maxims which I believe you, or others reading this comment, may benefit from:
Software is the manifestation of a solution
to a problem. Define the problem which needs
to be solved.
Developers can test their solution or Customers
will. Either way, the system will be tested.
Only progress a system from a known working
state to the next known working state. If the
current state of the system is unreliable
(IOW: "buggy"), peel back the existing logic
until it is in a provably working state.
Only then reintroduce removed logic (in
adherence with the above) to reach a working
state where additional logic can be introduced.
And, yes, it does matter "if there are mistakes" for the vast majority of software systems. Perhaps not those with which you've been exposed, but for many this is the case.
HTH