Assuming a lock is within the PC’s skill level, they will eventually pick the lock and get it open.

But if the room is filling with water or monsters are beating the snot out of the PCs, the question is not whether they succeed, but whether they succeed in five rounds. That is why it is not enough that success and failure are possible.

Again, this causes them to sometimes choose the wrong skill.

four dating rules-22

“I’ll give the door a solid, standing kick.” “I get a running start and jump over the chasm.” “I subtly offer the guard a bribe to let us pass.” The DM will ask for rolls as appropriate or determine the result some other way.

In the first situation, players often shoot themselves in the foot by trying to use specific skills in situations in which they are clueless.

If they are researching information in the library, they’ll eventually turn it up.

The trick is decide whether the PCs are constrained.

We also have to ask whether failure carries a cost or penalty.

In the case of the lock being picked while the room floods, the penalty for failure is death.

If the action is impossible, either because its just f$&%ing impossible or because the difficulty is so ridiculously high the player can’t succeed, don’t roll. This is actually trickier to figure out because a lot of actions seem like they can fail, but they really can’t.

Either tell the PC that it is impossible or narrate the failure. For example, if the PCs are ransacking a dungeon room, barring anything magically hidden or designed never to be found, they will turn up everything eventually.

The assumption is that, lacking any constraints, the party will keep trying something over and over until they succeed. When the party attempts an action, assume they mean to keep trying until it succeeds.