RE: Carve 121 set up
Learning to trust your rig and sail to hold up your entire body weight is not something easy to learn.
In fact it's completely foreign to those who have not actually experienced it.
We are basically land creatures, used to having our weight on our feet and legs.
When we try to "suspend" our entire body weight on something powered by a completely invisible force (the wind) it's pretty hard to convince both the body and the mind that this will actually work.
Drop your boom down a bit, maybe shorten your lines a little and pick a nice powered up day and go out and work on simply sailing back and forth on beam reaches with the sail/rig supporting you as much as your mind will allow.
Soon your mind will "adjust" to the feeling of being suspended by an invisible force and it will become easy to almost completely unweight the back of your board.
When you get all your weight on the rig, your feet just become the "steering mechanism", pushing and pulling to make your board do all the things you want it to.
All the weight and power are now transmitted from the rig down to the mast foot, which drives the board along in a much different way than if you have your weight on yout feet and much less mast foot pressure.
Get the harness line balance just right, and you can even remove your hands from the boom for a little while and have the rig just stand there, holding you up, as your board rips effortlessly (hey, how can you be expending any effort if there's no weight on your legs and the only thing attaching you to the rig is your harness..?).
It's fairly easy to "retrain" your body, but sometimes it takes a while for the mind to accept what the body is doing.
Hope this helps,