If a bald man grows just one hair on his head, he is still bald, right? If a billionaire gives away a dollar to a poor man, he's still rich. Even if he does it again, he's still rich and the poor man is still poor. A heap of sand may have a million grains of sand it in. Remove one, and it's still a heap (or in Greek, sōros). Remove another grain, and another, and it's still a heap. Is it still a heap when there are ten grains left. How about one? None? When does the heap cease to exist?
As is freely admitted, these are not precise categories. Therefore they will not have precise boundaries. One must accept that the truthfulness of P is not a yes or no thing. As N increases, then the truthfulness of P decreases and the truthfulness of not-P increases.
This means, for instance, that baldness decreases with increasing hair. A man with two hairs is very slightly less bald than man with one hair. By the time you get to a man with a hundred thousand hairs, he is not very bald at all. In fact he may be more not-bald than he is bald, and be somewhat hairy.