You are betting that a man who has had to split his training between kicks, knees, elbows, throws, rolls, ground work, locks, submissions and punches will beat a guy who since his early teens has done nothing but to home and develop reflexes in boxing.
That's like putting a triathalon in the 100m sprint against Bolt. Yes Bolt can trip over or be hit by a bolt of lightening and then loose :-)
RE: Mayweather will destroy McGreggor