Why are there holes all over the breakwater?

You'd think a breakwater should be sealed tight, but tetrapods have nearly half of their space empty. Instead of blocking waves with force, they let them pass through and dissipate their energy. As water flows in and out, the currents split and collide, gradually weakening the waves. There's also a reason why the four legs are spread out in all directions. When placed, three legs support the base, and the remaining one wedges between adjacent blocks, interlocking like clasped hands. This prevents them from being washed away alone when the waves pull at them.