A marinade is not random liquid. It is a tool.
At its simplest, a marinade is a controlled flavor environment. It surrounds food with salt, fat, aromatics, acid, spice, sweetness, enzymes, or fermented ingredients long enough to change the way that food tastes, smells, browns, or feels when eaten.
That does not mean marinades perform miracles. They do not usually penetrate deeply into thick pieces of meat or fish. Most of the action happens near the surface. But the surface matters. The surface is where the first bite happens. The surface is where browning happens. The surface is where salt, garlic, pepper, lemon, butter, herbs, smoke, soy, miso, mustard, ginger, and chili first meet heat.
The Most Important Truth About Marinades
Marinating does not usually make thick food deeply flavored all the way through.
That is why technique matters.
A thin salmon fillet, shrimp, chicken cutlet, sliced steak, pork tenderloin medallion, or scored chicken thigh gives the marinade more surface area. More surface area means more flavor. This is why cutting and shaping the food is often just as important as the marinade itself.
A thick steak left in marinade overnight may still taste mostly like steak inside. That is not failure. That is physics.
The solution is not always more time. Sometimes the solution is to cut thinner, score the surface, slice after cooking and sauce again, salt earlier, reserve a clean finishing sauce, or use a stronger surface treatment.
Good cooking is not just recipe-following. It is understanding what is actually happening.