ㄹ걸

Probably; or 'I should have'

Two meanings share this ending and the tense tells them apart. On a plain verb it is a confident guess: they probably won't know the direction, you won't hear it, I'm probably the tallest right now. On a past action it is regret about what you did not do: I should have drunk that coffee, maybe I should have just spoiled it, I regret not saying anything. Both are casual; adding 요 as in 모를걸요 makes the guess polite.

Register: casual