"If it ain't broke, don't fix it."
The problem comes when the rest of the world moves on, for example by retiring security cyphers that were in wide use at the time you implemented your software.
I don't like car analogies, but the demise of unleaded fuel meant you needed to apply some maintenance to older cars so that they'd continue to work in a post-leaded fuel world.
Biting the hand that feeds IT
