I'm usually in favor of the good old KISS principle, but I've experienced few situations where "simple" ready made solutions were chosen on the basis of few dem

I'm usually in favor of the good old KISS principle, but I've experienced few situations where "simple" ready made solutions were chosen on the basis of few demos showing "how simple it is to use this or that feature" over writing in-house scripts in general purpose language like python. In all of those unrelated situations there was trouble later when it transpired that indeed it is simple to use feature A, B and C that works exactly as original author's wanted, but the moment you want to tweak something manipulating the whole thing is terribly inefficient, and/or complex. In the end tweaking those simple ready made solutions required more work than re implementing the whole thing from scratch would take in the first place...