It’s not a Filipino invention either; most Asian countries have their own versions as well.
In the book “Palayok: Philippine Food Through Time, On Site, In The Pot” by noted food critic and cultural historian Doreen Fernandez, sawsawan is described as a “way of fine-tuning the taste of the dish to that of the individual diner.” It’s a way for us to be actively involved in the dining experience—a far cry from the French cuisine, wherein the chef has sole authority over the dish.
This explains why we have a sawsawan for every Filipino dish imaginable. We want our food not to be too salty, too sour, or too sweet so we have sauces to balance things out—like kalamansi for the salty pansit or patis for sweet dishes like tocino or lechon paksiw.
Interesting Trivia: The word toyo originated from the Fookienese term for soy sauce, pronounced as “taw-yu.” The Filipino word for vinegar (suka), on the other hand, was derived from either Chinese chho or the Sanskrit cukra which, when pronounced in Pakrit, sounds like its Tagalog counterpart.