When I first started training Brazilian jiu jitsu...it was quite an experience. The people were insanely warm and welcoming...and they threw me into a vomit inducing warm up. They were supportive and patient...and they paired me to spar with a bear of a man within a week. As an art, Brazilian jiu jitsu has an insanely high rate of attrition--it's estimated around 90% at each belt level. People aren't getting kicked out or failing. It's just that hard to stick with. I couldn't understand why, two months into training, I was begging to sign a contract, but the head instructor still wouldn't let me. "Are you sure?" I was asked over and over again.
I sometimes wonder what would happen if churches functioned in a similar manner. I'm not saying they should...I'm not even sure how you'd implement that, but to this day, I wonder.