It is known that the strong interaction is responsible for the existence of the proton. However, it is really difficult to theoretically deal with it in the low energy regime where matter lies. This is a fundamental problem which also impacts new physics searches. A clever solution consists in taking advantage of a certain invariance: this is what Chiral Perturbation Theory does.
Come for a layman's introduction to the topic and cool symmetries (almost like Omar's, but in 4D).