So many designs in engineering look great on paper or in a model, but in the real world they may fail or not be able to exist because the material can be too weak, unforeseen issues can come up, and so many other things can prevent something from working. This is the exact same in the real world. This issue occurs with just about anything that involves something bad not happening. Plenty of things seem amazing on paper, but in practice, they do not work either as good or at all.