The defensive side needs everything to go right, all the time. The offensive side only needs something to go wrong once.
It's a subtle difference from what you said in that it's not like everything has to go right in a sequence for the defensive side, defenders just have to hope they committed enough into searching such that the offensive side has a significantly lowered chance of finding solutions they did not. Both the attackers and defenders are attacking a target program and sampling the same distribution for attacks, it's just that the defender is also iterating on patching any found exploits until their budget is exhausted.
It's probably more worrying as you get script kiddies on steroids which can spawn all around with same mindset as even the dumbest significant geopolitical actor out there.