If the outcome is in doubt and there is a meaningful consequence for failure, then an ability check is called for.
So if I describe the orc engaging in a great display of intimidation, the next step is for the player to decide success, failure or doubt. If the player says, "The orc's display makes me a bit nervous, but I cannot be cowed," then the intimidation has failed. If the player says, "Holy cow. I don't want to mess with that guy. I turn around and run back into the forest and try to get away, " the intimidation has succeeded. If the player says, "That's a really impressive display, I'm really not sure if I would stay or run," then a roll is called for because the outcome is in doubt and there is a meaningful consequence for failure.