I think you do whatever it takes to achieve correctness.
If simplicity helps achieve correctness, then great.
But correctness is not always simple.
Most people think there is a leap year every four years. They are wrong.
If simplicity helps achieve correctness, then great.
But correctness is not always simple.
Most people think there is a leap year every four years. They are wrong.
In their minds, when things stop being simple, fast trumps correct.
If I'm writing a file backup program, it absolutely must back up all the files without leaving any out or corrupting the data.
But let's say it has a feature that prints progress indicator percentages on the command line, ranging from 0% to 100%. Maybe under certain circumstances (like files added to a directory after the backup starts), it prints 102%. It's not what I had in mind, nor is it something I'd call correct. But if fixing it complicates the code a lot, maybe leaving it that way is the better choice.
(This is a bit of a contrived example because you could just clip the value at 100, but you get the idea.)
Abstraction allows you to hide complexity and make it a simple, reusable part again.
Plus, a complete leap year implementation is already what I would consider simple and most standard libraries already have an implementation for it you can use directly.