But if the Level 1 party positively insists on walking up to an Ancient Red Dragon and poking it with a stick, they'll die. If they stick to the safest areas and pick on goblins, they'll be fine, but won't learn much. If they seek out things that seem challenging but play cleverly and with proper planning, they might get huge rewards. Obviously you cook the books a little with random encounters, but even there, maybe by good luck there'll be something they defeat easily, or by bad luck be something they need to flee.

The world doesn't revolve around them. It can't all be mother-may-I, or you may as well write a novel.

If a character rolls a 3 - well, personally in the case of Knowledge I'd let them take 10, old-school, if not threatened, reasoning that the roll is for things you may or may not know or recalling things under pressure. But the point of the 3 is that it's some fact that they just don't happen to know, so they have to go and find out.