If I leave the house I'm carrying. I have been doing it quite a while now and it has become so ingrained in me to carry that I never forget my pistol but frequently forget my cell phone. As far as getting involved in stopping a robbery, I don't know. Look at what happened to the bodega owner in New York. Defending himself from an assault and robbery, ending up getting jailed without bail and charged with murder. If I thought that the thug was going to kill someone then I probably would get involved hoping and praying that I didn't get charged with shooting someone.
The bodega case is a strange one. The aggressor tried to pay for some chips with plastic. When the card was refused, the store owner retrieved a bag of chips back from a child. The aggressor came behind the counter to try and get the store owner to apologize, but with force.
The owner responded with a knife, he was also stabbed in the arm by the perp's girlfriend. The perp had done prison time for a previous assault, getting sent to prison in NY meant it had to be a pretty serious assault.
The store owner initially had bail set at $500K, the NYC mayor got involved and talked to the Manhattan DA, and suddenly the bail was dropped to $50K, and the store owner walked that night.
The perp's relatives gave the usual story, "he was turning his life around, he said his previous jail time would be his last". Well, obviously he didn't remember that when he used force. Although in NY you have a duty to retreat, there was no place behind the crowded counter to retreat to.
Be interesting to see if a grand jury will indict the store owner.
As for me, I try and carry every time I'm out. I know I'd feel stupid if the one time I didn't carry, something happened. That is, if I survived the incident.