Go force on force against an opponent who can absorb your force, whether due to size, strength or skill, then all you're doing is bleeding energy into them or through them.
If they give something into the system however ..... whether through momentum or because their center of balance is off, you have something to play with.
And there is almost always some kind of movement in the system ... they can't strike or throw you without moving, and if there is no movement in the system ... usually it means nothing is happening, so maybe nothing needs doing. Even if it is a very bad position for you, still you must create, or wait for, movement in the stronger part of the equation to be able to change it significantly.
Most martial arts talk about this - using the other person's force against them, but for some reason it's incredibly hard to access, especially if you think you are losing ....
Last weekend Rory Miller was in town again, and I got to play with a bunch of new people.
Because the drills, by their nature, are practiced in a non compliant manner, any disparity in size or skill becomes apparent quite quickly. The bigger the disparity, the more the above applies. Play with someone skilled at joint locks, twice your weight, 6 inches taller, with a great root ... and you better believe that it's better to avoid resisting their force, because whatever you give into the system they can either just absorb, or use against you, whereas you cannot absorb what they give to you. You have to go with it and wait for the right ma-ai when you can use the space that is available around what's happening to redirect, slip, trip, or counter.
The lesson is, tense up and resist what's happening and you will exhaust yourself pretty fast. Relax, notice the emptiness and the potentials, and you can prevail.
This same tendency to tense up and resist what's happening, occurs in dueling also.
New students tend to play with their blade out in middle ground, desperately covering and blocking anything that comes into view.
This of course seems to make a great deal of sense, but tactically it's a bad idea, mostly because you are behind the timing, and giving unnecessary contact over unimportant non-threats creates openings, or worse, just makes bridges to the target instead.
Purposefully seeking contact is, of course, a way to create potential opportunity for yourself. Bagua does it by forcing contact through offense or defense - you threaten or block, and work with the meeting force to create your attack - circle meets line.
Another example would be when one blade leans against another, and through the contact point manipulates the opponent into an error - I push on you, you push back, I slip under and strike the opening caused by the spring load - many applications of this in Toyama Ryu, Fencing, and Eskrima.
Of course if you don't want to be taken advantage of this way, you have to practice relaxing into the contact point, going with the force, reversing the advantage (often by taking center first), or not giving contact at all ... especially with swords.
Really, in dueling, the opponent should never feel your contact unless you have screwed up and are blocking, baiting to cause a reaction, or deflecting AS an entry. In other words 'with purpose'.
Sonny said many times - "Let them come. They are coming anyway. Don't push them/keep them out. Invite them in and control the game".
What this means essentially is being open, taking the weapon out of the game, away from target, seeming defenseless.
When I first tried this I thought, like most other beginners, that it was one of the most counter intuitive things I'd ever heard. But, as it turns out, it works quite well .... but only if you can exploit the potential reactions that manifest from what you offer, from getting your opponent to commit, and move.
The ability to be comfortable with this idea enables practitioners of throwing arts to do reversals and sacrifice throws. It enables practitioners of striking arts to fold joints, climb up, slip and counter, grappling artists to roll out and reverse locks, and duelists to become ghosts.
Everything is a gift.