Why it happens
Sweetness comes from sugar and sweet ingredients such as honey, onions cooked down for a long time, sweet vegetables or fruit. Once sugar is in a dish you can't take it out, but you can change how sweet it seems. Acid, salt, bitterness and chilli heat all balance sweetness, so adding a little of these makes the dish taste less sugary. Diluting the dish with more of its other ingredients lowers the sweetness directly. Baked goods are harder to fix after baking, because the sugar is part of their structure.