Jose Mourinho claims a "nice guy" manager can end up becoming a "puppet".
In what could be construed as a swipe at his Manchester United successor Ole Gunnar Solskjaer, Mourinho says time has proved his methods at Old Trafford were not the problem.
Mourinho, who led United to second in the Premier League last season, was sacked in December after a dismal start to the latest campaign.
Solskjaer brought a fresh approach and lifted a lot of the gloom after taking over on an interim basis, winning 10 of his first 11 games, but form then deserted him after being appointed full-time.
United won just two of their last nine league games and finished in sixth, outside the Champions League positions.
Mourinho told L'Equipe: "Generally, the players can feel a certain erosion, especially when you ask a lot of them.
"When I say that the second season was fantastic, I say it because the potential and the objectives were met.
"I really squeezed, like an orange, to achieve them. When you have a very professional group of players who are ambitious, hard-working and talented, at a structured club, you don't have that erosion.
"When you are almost alone, in that you don't have the support of the club close to you, while certain players go somewhat against the coach, who is the nice guy.
"I don't want to be the nice guy, because the nice guy, after three months, is a puppet and that doesn't end well."
Mourinho continues to rate last season's second place highly - when United finished 19 points behind Manchester City - and feels recent events have cast it in a greater light.
The former Chelsea and Real Madrid boss said: "I said nine or 10 months ago that after winning eight championships, finishing second with United may have been my greatest achievement. Now people understand.
"About United I want to say only two things: One is that time has spoken. Two is that the problems are still there."
Mourinho reportedly had his differences with record signing Paul Pogba, but he insists the problems at the club go far deeper than the France midfielder.
He said: "The problems are there, you can say that these are the players, the organisation, the ambition. I only say that I cannot say 'yes' when you ask if Paul was the only one responsible."
Meanwhile, Barcelona are tracking Angel Gomes as he approaches the final year of his United contract.
Gomes, 18, has generated interest from clubs across Europe since making his United debut at the age of 16 years and 263 days against Crystal Palace in May 2017 and is out of contract in 2020.
The Salford-raised playmaker has only made three additional substitute appearances since his first-team bow and Gomes had a loan moved lined up in January.
United manager Ole Gunnar Solskjaer, who played Gomes in his first Old Trafford match in charge against Huddersfield, blocked Gomes' departure in the winter window but only sent him on again in the final game of the season against Cardiff. Mason Greenwood, who is a year younger than Gomes, has already made his full debut.
Gomes was named as a substitute in the 3-2 win over Southampton, as well as the 3-1 Champions League second leg triumph over Paris Saint-Germain in March, and was included in a handful of provisional squads but failed to make the matchday squads. He started 16 times for the Under-23s and U19s, scoring eight times.
Mourinho named Gomes in the pre-season tour squad last year and the expectation is Gomes will travel to Australasia with the first-team this summer. Solskjaer has already indicated United youngsters will figure in the Europa League next season but omitted Gomes from his list.