I did a lot of "naked* into the wilderness"-style survival training when I was younger. It showed me that I could reach what I thought were my absolute limits of physical and mental exhaustion, and then push far past them. It changed me from someone who frequently gave up to someone who doesn't give up.
This school[1] is a good place to start (though I haven't been there since the 1990s). I highly recommend this kind of wilderness training.
* not literally naked, but meaning that the goal is to remove the equipment-lifeline back to society. No gear is allowed except what you create yourself (stone knives, brain-tanned deer hide, etc.).