One of the defining principles of Brazilian Jiu-Jitsu is the use of leverage to overcome physical advantages. Rather than meeting force with force, practitioners learn how to use body positioning, weight distribution, angles, and mechanical advantage to control opponents more efficiently.
This does not mean strength is unimportant. Size, power, and athleticism will always matter in a physical contest. However, BJJ seeks to reduce these advantages and make technique the deciding factor whenever possible.