The most useful cooking skill is diagnosing what a dish is missing, and it comes down to a small number of possibilities that can be checked systematically.
The five directions
Salt, acid, sweetness, fat and heat cover almost everything.
Which means tasting and asking which of these is short is a reliable procedure rather than a matter of intuition.
Umami and aroma are the further two, and they are less frequently the missing element.
Salt
The most common deficiency by a wide margin.
Salt suppresses bitterness and enhances the perception of other flavours, which means a dish tasting flat is usually undersalted rather than lacking an ingredient.
Adding gradually and tasting between additions is the method, since it cannot be removed.
Salt added early penetrates and seasons throughout. Salt added at the end sits on the surface and tastes sharper, which is why finishing salt exists as a category.
Acid
The second most common and the least recognised.
A dish that tastes heavy, dull or cloying generally needs acid rather than more seasoning.
Lemon, vinegar, tamarind, yoghurt, tomato and wine all contribute it with different characters.
The test is adding a small amount to a spoonful in a separate dish and tasting the difference, which avoids committing the whole pot.
Sweetness
Balances acidity and bitterness rather than making a dish sweet.
Which is why a small amount of sugar in a tomato sauce works, and why it should be undetectable as sweetness.
Onions cooked long and slowly provide it without sugar, as do carrots and other sweet vegetables.
Fat
Carries flavour compounds and coats the palate, which changes both intensity and duration.
A dish that tastes thin frequently needs fat rather than more of anything else.
Butter, oil, cream, coconut milk, nuts and cheese all do this differently.
Heat and aromatics
Chilli, pepper and pungent spices add a dimension that is separate from flavour.
Fresh herbs added at the end contribute volatile aroma that cooking destroys.
Which is why the same herb tastes entirely different added at the start and at the finish.
Fixing over-seasoning
Too salty is genuinely hard to fix, and the traditional potato remedy has been tested and does not work as claimed.
Dilution with more of the unsalted components is the reliable approach, and adding acid or fat can mask it somewhat.
Too acidic is corrected with sweetness or fat.
Too spicy is corrected with dairy, fat, starch or dilution.
Too sweet is corrected with acid or salt.
Practical technique
Taste from a spoon rather than the cooking implement, and use a clean one each time.
Taste when the dish is at the temperature it will be served, since perception changes with temperature substantially.
Test adjustments on a small portion before committing.
And taste at intervals throughout cooking rather than only at the end, since problems are easier to correct early.
Palate fatigue
Repeated tasting of the same thing reduces sensitivity to it.
Which is why a cook who has been tasting a dish for an hour is a poor judge of it, and why asking someone else produces useful information.
Water, plain bread, or a pause all restore sensitivity partially.
Bitterness
The one direction that is hard to add deliberately and easy to acquire accidentally.
Burnt garlic, over-toasted spices, over-extracted coffee and certain vegetables all contribute it.
Salt suppresses the perception of bitterness, which is one reason a bitter dish can be improved with seasoning.
Fat and sweetness also mask it, and none of them removes it.
Temperature and perception
Cold suppresses aroma and sweetness perception while leaving saltiness and bitterness more prominent.
Which is why a dish seasoned when hot tastes different cold, and why anything served chilled requires more seasoning than it seemed to need.
Ice cream base tasted warm should taste too sweet, since it will not once frozen.
Layering acidity
Different acids have different characters — vinegar sharp, citrus bright, tamarind fruity, yoghurt gentle, wine complex.
Which means the choice matters beyond the sourness, and using more than one produces depth that a single one does not.
Writing it down
Noting what was added and how much converts a good result into something repeatable.
Which is the difference between cooking well occasionally and cooking well consistently.
Aroma
Most of what is perceived as flavour is smell rather than taste, which is why food tastes flat when the nose is blocked.
Which means aromatic additions — herbs, citrus zest, spices, a final drizzle of good oil — contribute more than their quantity suggests.
They are also the first thing lost to prolonged cooking, which is the argument for adding them at the end.
Serving context
A dish tasted alone is not a dish eaten with rice, bread or other components.
Which means the seasoning should be judged against how it will actually be eaten, and a sauce that seems too intense alone may be correct.