Yes, it was Man Utd's hard work when facing a strong team at the moment, but I think Liverpool didn't put all their energy into this match because Liverpool was more focused on the EPL and UEL competitions, so even though they lost in the quarter-finals of the FA Cup, it doesn't change the possibility that Liverpool still strong and this defeat against Man Utd can be a lesson for Liverpool not to underestimate teams that are not very consistent because sometimes teams like that can give surprises, Man Utd finally qualified for the semifinals and I think Man Utd can reach the final and fight Man City to win the trophy.
Liverpool did invested that energy and strength but then there are points where energies and strengths could be in matching and when they are, you are most definitely not going to be able to get beyond how well the strength could take you a d that was exactly the case of Liverpool as they did all they could having the matching energy and strength yet they couldn't win because at some point they taught it was over.
Thinking it was over and altering the strategy was what caused Liverpool that game and now they are suffering the consequences thereafter because actually in that game , Manchester united actually weren't doing much enough so invariably, Liverpool was actually deserving of their wins in the game already and they just needed that sustainability till the end, I was even thinking Liverpool would be able to net a goal in the second half following the sequence with which they got their goals in the first it looked like they were ready to show some more in the second half.
Manchester united actually got the opportunity to get the only goal that was scored in the second half before the extra time, I had taught this game wasn't going in to an extra time because Manchester united looked like they were going to loose the game already until they had their second goal and almost the third which rashford did missed in the last minute of the game, the match would have ended in a goal as the final whistle goes.