I like Sig's explanation of MBM.
I think there is more.
The receiver also has to have an understanding of what the official is going to call a penalty and how to be able get away with small nudges and pushoffs when contesting a ball. It's the game within the game and a subtle art of getting away with as much as you can.
A lot of receivers can run great routes and show discipline in timing patterns. But It's the MBM receivers who adjust in midflight of errant passes and like cats adjust their hips to take akward angles to the ball, often through the defenders basket. Outstanding body control and ability to switch up hand position to snare a ball off the hips or at the defenders ears, generally extending the arms in any direction as an extending receiving diameter. Those are the "F-U, it's my damn ball" guys. It's an instinct that can't be taught, mostly because its complex to operate that many body muscles in the wink of an eye. The elite ones can do it, and the run of the mill ones get it swatted away or intercepted. It's the MBM guys that maximize their targets because they catch the balls they aren't supposed to.