Constant Forward Pressure

There are things about fighting that are very difficult to learn without fighting. There are things about an assault that are difficult, maybe impossible, to learn without being on both ends of an assault. Martial arts training is largely about trying to preserve and pass on skills without the side-effects of using the skills. You want to learn to punch without the arthritis from old fractures in the delicate bones of your hand. To learn how to survive an attack without the accumulated concussions and microconcussions that are a natural result of knowing what "surviving an attack" even means.

When we sanitize fighting and try to make it safe we lose a lot of information. In hierarchical systems, if information is lost to one generation of instructors, the system tends to resist the information when it is rediscovered.

Some of those little bits of wisdom are so obvious it feels weird to talk or write about them. This is one.

Hitting changes stuff. Not just 'hitting a body feels different than hitting a heavy bag or punching air.' Every time you hit or are hit for real, something changes. Something in the structure of the person receiving the hit is disrupted. If you get hit hard enough in the face to twist you neck, it will change your shoulder alignment and the distribution of balance between your feet. If you take a heavy rising body blow it can break your connection with the ground.

Every incoming impact affects you, and every impact you deliver affects the threat.

In order to hit well you need power, targeting, timing, and empty space to move through.
Power is usually based on structure and a connection with the ground OR whip action and speed.
Targets must be in range and available. If you can't reach it you can't hurt it.
I'll skip timing. Timing in fighting is a complicated art form, in assault (either doing or receiving) timing is dead simple.
Empty space is something an infighter must manage.

Every solid impact affects at least one of those things. It can disrupt structure and connection with the ground and interrupt the looseness required for whip power. Changing structure changes range and the body's orientation to available targets. Attacks change your perception of time and thus alter your timing.

The essence of defense is to disrupt the other person's offense-- by denying targets or disrupting, power, targeting, timing or range. "The best defense is a good offense" is a literal truth when you are working with impact.

On the receiving end it is a double-whammy and almost impossible to understand or get skilled at without experience. Incoming attacks at power mess you up physically, as described, but also mentally. Fast hard attacks disrupt your OODA loop and tend to overwhelm people into a passive, child-like mode. The determination to keep control of your own mind and to adapt to the physical disruption-- there are exercises which can show you pieces of it (Infighting randori is the best I know, followed closely by full blown scenarios...) but the real thing can't be replicated safely.

I first heard "constant forward pressure" as a wing chun strategy. This is my understanding of it today: Every attack disrupts. Each contact does damage; disrupts the threat's targeting, timing and distancing; and sets up the next shot. (I tend to fight by touch instead of sight, so indexing and pivoting the attacking limb off the point of impact are big for me.)

Constant forward pressure lets your offense handle your defense. It sounds like an armchair strategy, but it is an obvious natural truth when you are hitting and getting hit hard.