#1 Player-coach management
Mourinho does not always handle his players in the best manner possible.
In every team, there are key players who can decide games and lead the rest. Pogba happens to be that kind of player for United. He was bought for a world record fee due to his technical ability and mastery of the game, and would expect a certain degree of leadership responsibility on his shoulders.
Pogba was Mourinho's biggest signing, a player that could have been the poster boy of his success. He had left a club that dominated Italian football and was on the cusp of conquering Europe, because he expected better at United.
However, Mourinho has since taken several swings at him publicly over his performances. He also froze Pogba from the first XI last season, for no discernible reason.
Since then, it has been a bitter-sweet relationship between the two. Mourinho even stripped Pogba of the vice-captaincy, which added fuel to the fire.