“We're not good enough or strong enough because we're not winning, and we're not good enough or strong enough to score the goals we should,” said the United boss.
“We're giving the opponents and their goalkeeper the chance to be man of the match so many times.
“But I still think in spite of bad results - because for us a draw is a bad result – we're strong at home.
“Why? Because we've only lost one game, a game we know why we lost.”
Mourinho believes their opponents' more cautious approach at Old Trafford has convinced him a return to United's trophy-laden era under Sir Alex Ferguson could be in the pipeline.
“What makes me think we're strong is the way opponents play against us because that's a big change,” he said.
“I saw matches in previous seasons when teams came to Old Trafford thinking they thought they could win, they played an open game and played an 'eye in the eye game' and many times lost with a counter-attack goal.
“I've watched and analysed Anthony Martial and Marcus Rashford's counter-attacking goals and it's impossible for us to score in a counter attack because teams come to Old Trafford thinking not about winning but about not losing.
“Looking to next season, I think it's a good feeling to know we haven't lost many matches.
“It's good to know we're 20 matches undefeated in the Premier League. Ten draws in 10 matches is 10 points; five victories and five defeats in 10 matches is 15 points.
“But the points are the reality.”
The 24-year-old England international has committed his future to United until 2021.
The award of such a lucrative contract to a squad player who has played just 70 times with just one Premier League goal this season has posed questions asking if younger players have the hunger to succeed.
But Mourinho said: “I think he's a good player already and because of his age and happiness in the work, I think he has conditions to be even better.
“Apart from that, he's English, he's made in the academy which is very important.
“So it's a very important contract and I congratulate him and the board to reward him with it.
“It also gives stability for me, because it's important for me to know that (his future) is not in danger and out of our control.”
Mourinho was non-committal over the future of Adnan Januzaj.
Januzaj has failed to impress in a season-long loan at bottom club Sunderland, and was booed when he was substituted in Saturday's 1-0 defeat at Watford.
The 22-year-old's contract is up in just over a year's time. Asked about the player's future, Mourinho said: “Yes, I have decided” but refused to elaborate any further.
United's opponents in Sunday, Sunderland, are 10 points from safety in bottom place with eight games left.
Mourinho expressed sympathy to Black Cats manager David Moyes, one of his predecessors at Old Trafford.
“I have sympathy for any manager that is fighting hard to reach his objectives, and he's in trouble to do it,” he said.
Wayne Rooney (ankle) is unavailable, Ashley Young (groin) is doubtful and Juan Mata, Chris Smalling and Phil Jones have long-term injuries.