The sentence in the title is inspired by a sentence on the gate of hell in Dante Alighieri's masterwork Divine Comedy (Part I: Inferno). I usually write it on my office door after exams when I think there are some requests of failed students for a remedial exam. It illustrates that I don't accept such requests. Recently I thought it is not bad to be more flexible about this situation.
Question: What is the best policy about requests of students for remedial exams (or more time for their homework)? Are there situations that a teacher should consider such remedial opportunities? Should I replace the sentence on my office door with "Never say never!"?