Walk into a restaurant. Sit down. Review the menu. Order food in Spanish or in English, or a tourist mix of both. Wait.
This sequence is similar to everywhere else in the world. The ordered food will begin to arrive, along with a small dish or two not ordered the condiment. It is the reason for the rest of the food. Aji.
Not ordered, but graciously served, aji, a sauce made from local chills of which there are many varieties, goes with everything savory. All the other foods (potatoes, rice, french fries, eggs, onions, cooked vegetables, quinoa, any kind of meat from alpaca to cuy to chicken to fish) are only substrates to convey to the mouth, to the tongue, the complex savor of aji. It is almost impossible to get enough, even though a little goes a very long way.
Though the majority of this dining experience is similar the world over, aji is not. This delicacy, and I do mean delicacy even though it is as common as corn syrup in the US, is exclusive to Peru. It is handmade, from fresh peppers, herbs, onions, perhaps cheese, some spices. And though it is always sered, there are as many ajis throughout the cities, towns and homes of Peru as there are restaurants and grandmothers. Though there are common ingredients, every one is unique, nuanced. The reason for eating in Peru; to taste aji.