Some are being too cynical about this.
When United won the Premier League and Champions League double in 07/08, United lost to Portsmouth in the 6th round of the FA Cup (at home mind you). That was bizarre the fact 99% of all people would have fancied United to FA Cup glory because the team was that superior to the other semi-finalists in West Brom, Cardiff and Barnsley. Obviously there is too much hindsight in this saying United would have been Treble winners once again, however that was a great FA Cup run.
A club of United's stature, the standards are always win what you're in. Europa League, Premier League, FA Cup, League Cup, etc. Achieving the ultimate goal of winning a competition should never detract from what you've accomplished. 19 teams will not will the Premier League. If United finish 2nd this year let's say, it would be deemed successful. But ultimately, not the ultimate goal/success and certainly you'll hear that from LVG and players.
When United lost to AC Milan in CL semi-finals in 06/07, that was a success because the team made a run that wasn't really expected in the CL. But we saw the progress made by Ronaldo and Rooney and team to really make a run the next year or two or three. Sure there's massive disappointment, but you have to include some realistic perspective.