What is considered grammatically infelicitous about 'Illud mōnstrum tam horribile vīsū erat nē hominēs fugere possent.'?

The phrase 'Illud mōnstrum tam horribile vīsū erat nē hominēs fugere possent.' contains a grammatical issue related to the use of 'nē.' In Latin, 'nē' is typically used to express purpose in a negative context and translates to 'so that... not.' However, in the context of this sentence, which intends to convey that the horrible sight of the monster prevented people from fleeing, 'ut nōn' would be more appropriate.

Using 'ut nōn' would correctly frame the intended purpose—indicating that the monster was so horrifying that it caused people to not be able to flee, rather than it implying an outright prohibition. Thus, 'ut nōn' would properly convey the negative purpose while maintaining grammatical correctness.