Also to not give up on them. He easily could have seen the defender between him and the ball and held off his run. Instead he stepped on the gas and was determined to give it every chance to get there.
That's what I was saying earlier. So many United players have a passive mentality like Sancho or Martial. If the play isn't there, they'll just coast a bit. Garnacho seems to want to give 100% on every single play even if it looks dead.
Obviously he's got plenty of skill as well, but the effort is what makes the big difference.