When it is said that a detail makes the difference. The phrase "for a point Martin lost the hood" refers to this.
What is the history of this proverb? The phrase was originally "to a single point Martino lost Asello" and refers to the mishap that hit Martin, Friar of 1500, due to a punctuation mark.
The abbot decided to make decorative improvements to the monastery of Asello, I think I'll affix wooden planks on the door with a phrase of welcome. The craftsman that commissioned this work, because of a distraction, was mistaken punctuation and therefore the meaning of the sentence.
The mistake caused serious problems to the Abbot wanted not because the message written on the threshold of the Abbey had become anything but welcome and definitely against Christian morality. High ecclesia decreed that Martin was no longer worthy of the religious endowment and deprived him of the cowl, typical symbol of the Office of prior.
So "For a point Martin lost the cowl" is a curious way of saying that means that one minor mistake can lead to the disastrous consequences.