Rory MacDonald lost his second UFC fight to Carlos Condit, and one of the reasons he felt he came up short was getting too emotional from his home crowd in Vancouver, and consequently gassing out towards the end of the fight and getting battered in the third round. However, MacDonald learned a valuable lesson that day about controlling his emotions, and from then on he has taken the direct opposite approach about being very dispassionate and unemotional about his work in the cage, and just executing his technique in the finest form possible.
In an interesting book Making Sense of Sports by Ernest Ellis and Ernest Cashmore, the authors noted that mentally tough athletes are not emotionless but very adept at shutting out this distractions in competition:
Many fighters are very good at keeping their emotions at check in the cage. For instance Ronda Rousey, through her thousands of matches in Judo has learned how to fine tune her emotional state to achieve peak levels of performance in combat. Conor McGregor, the Irish UFC featherweight star also banishes emotions but rather takes a calm and creative approach to his fighting. Some fighters however do get fueled by emotion and it works for them; such as Diego Sanchez and Benson Henderson, who admits he is an emotional person and needs to draw upon that to get into peak performance state. Additionally, Michael Bisping seems to get a special edge from anger, and even when he was competing against his nemesis Jorge Rivera, in between rounds he was fuelled by anger. So there is no hard and fast rules to this that one must absolutely follow, but for general best practices it's often a good thing to avoid emotions in competition, especially anger, which as coach John Danaher says, "Anger just makes people inefficient. Their breathing gets shallow, they're too muscularly tense; they gas faster."
