I only hit to the beans but not the laffy taffy and bedrock. Why I am so weak to cut myself brutally.
The same reasons people can't CTB easily. Survival instinct.
Often our brains can handle a lot of pain but once you hit a certain threshold (that is different for everyone) it blocks you from hurting yourself worse. It's all self preservation tactics ingrained into humanity for generations.
The only two ways I've ever herd of getting over it is: either you condition yourself out of it by building very slowly over your limits or you hit a breakdown so bad that you shatter the barrier by complete accident.
Wouldn't recommend risking it for your chances to CTB tho. I'm on SH forums and a lot of the people who have the worst wounds (3rd degree burns, narcotic skin, purposeful infection, permanent nerve damage, muscle and bone-deep cuts, etc.) all have been sectioned for it at one point or another. Some even post from in a ward.