We are prediction machines. In other words, our brains are constantly running simulations of how things might unfold - in the near term, long term, and points in-between. These ongoing calculations shape what we feel, think, and do.
Predictions are not created equal. Some feel like sure things; others like guesswork. When we lack confidence in our ability to predict the consequences of our actions, it's hard to act decisively. If out of temperament or situation we want to act decisively but lack such confidence, we may use some rule of thumb to move forward. One rule of thumb is "go with the gut", which basically means to follow one's intuition in the sense of "keen and quick insight".
Rule of thumb = heuristic.
Moral intuitions aren't enough to guide moral decision-making. We also have to consider the consequences of our possible decisions. Often we just intuit the consequences: action 'x' will make the situation worse, or make it better. The process goes something like this: sense the moral issues at play, consider possible actions, intuit how each action-decision would pan out, and then go with what feels like the best option, with the best result.
Ah, but that sounds too effortful for the intuiting fast brain, and sometimes it is. But often it isn't, because we simply rely on further heuristics to simplify the moral decision. If these additional heuristics were put into words, they may sound like "when in doubt, go with tough love" or "when in doubt, provide relief". Note how uncertainty ("when in doubt") calls for heuristic assistance. Help! I need a heuristic! Thinking hard is aversive!
One could have a heuristic to jump out of the fast and easy into the effortful, something like, "If you're not sure, pause - then think it through". That "pause" is a fast brain trigger for the slow brain to take over.