Practicing MMA (but any single art like Boxing, Wrestling, Muy Thai, etc would work) has definitely boosted my mental toughness. Once you step into a ring with someone who is trying to attack you, and come out okay, you realize you can handle pretty much anything.
Even if you don't spar, simply motivating yourself to go to practice can be tough. If you can walk into a room knowing you're going to be pinned and choked, you can walk into an interview/negotiation/meeting/date no problem.
Even if you don't spar, simply motivating yourself to go to practice can be tough. If you can walk into a room knowing you're going to be pinned and choked, you can walk into an interview/negotiation/meeting/date no problem.