Mourinho admitted that he used to obsess over every result but has now found a better balance and perspective, which has helped him keep his cool under pressure.
The Portuguese has already been in trouble with the Football Association this season, regarding incidents during games against West Ham, Liverpool and Burnley, but he insists he is now more tranquil.
When asked what he has become since taking over at United, he told France Football: "I would say, 'The Calm One.'
"Everyone expected me to be a problem. But the only problem I've had up till now is when I kicked a bottle of water in front of me [against West Ham in reaction to Paul Pogba being booked]. I was sent to the stand and had to pay a fine for that.
"That's my problem: when I'm a little bit frustrated, I kick bottles. But it's my only outburst since my arrival eight months ago. So, I have become 'The Calm One.' Having said that, perhaps tomorrow I'll get sent off.
"Today, I feel good with my personality as a man. I have matured, I am more peaceful. A victory no longer represents the moon, and a defeat hell.
"I believe that I am able to transmit this serenity to those who work with me, to my players. I have the same ambitions as before. The same involvement, the same professionalism, but I'm more in control of my emotions."