You have to be able to talk through your issues Grape.
If someone pulls a gun you should calmly ask if they think they making the right decision. Violence is never the answer, unless you’re the star of an Amazon prime show and it’s pretend.
You have to be able to decide if something is worth risking your life for.
Reacher had no way of knowing if this guy had a concealed knife or gun. Reacher should have quickly analyzed the situation and decided if it was worth risking the possibility of being stabbed or shot in front of his family. Reacher's life wasn't in danger at any time. The old man was angry and a hot head. No one was hurt. Only Reacher's ego was hurt.
What if Reacher had just stepped back away from the old guy and guarded his kids? He could have diffused it all. Instead, he left his kids wide open for an attack. What if the guy began shooting after Reacher started wailing on him?
What if the guy had a heart attack after getting punched? Would the police review the footage and decide the level of force Reacher brought was equal to the original perceived threat? NOPE. Pretty sure Reacher would be charged with murder and goodbye Hollywood Hills.
Each time someone lets their anger and emotions in the moment control them, there's always the risk of a worst case scenario.
Look at the incidents of people on the subway telling someone to be quiet, and then getting stabbed, shot, or set on fire. Or the PA neighbors arguing about snow shoveling and getting shot. Or the woman who yelled at the man to stop playing his music son loud at night and he burned her house down as she slept.