It's not just about cracking under pressure as a whole like in a sport. You're going to be constantly putting yourself into new and uncomfortable positions. The first time you get a guy (or I guess gal) who massively outweighs you in north/south position and smothers your face with the girth of their chest or stomachs, it will suck. You really can not breath then. You'll have your face sat on. You'll have your gi pulled over your face which just make breathing harder. If it's just a one time thing for you, then great, but don't expect it to just be only this one time.