The first time I heard the quote was in an article about Clint Smith/Thunder Ranch. I think the whole quote is "A handgun is for fighting your way to your rifle which you shouldn't have put down in the first place"
To answer jdd's original question:
Depending on whose study you read, Good guy has gun, bad guy gives up or leaves or otherwise the situation is okeedokee in 6 out of 7, 13 out of 14, or 33 out of 34 criminal situations.
But if your number comes up where you're the 1 in 7, or 1 in 14, or 1 in 34, then a handgun is always good to have, but if you ever have a choice then you want a long arm. (long arm AND handgun is good to have).
Handguns wounds cause death in something like 30% of situations. (Can't remember where I saw that.) Rifles/shotguns cause death in 70%+ of situations. I'm not trying to say we're trying to kill the bad guy(s), but obviously one is much more decisive than the other! (Side note: we shoot to STOP the threat).
This is just my opinion, but I don't want to have a minimal amount of power to stop the bad guy. I want a comfy margin of safety in MY favor. Also, bad guys are coming by the carload more often nowadays. I surely don't want minimal power if 5 perps are forcing the issue.
Aside from the power issue, long arms are much easier to aim with less practice than handguns. At very close range handguns have an edge, but if you have time to prep your situation by maybe getting behind furniture and covering the doorway, or maybe behind your car with your hood to brace on with the bad guys a comfortable distance away, the long arm is MUCH easier to hit with.
...but don't forsake handguns for all these reasons. Rifles don't replace handguns, they complement each other.
Hope that helps.
Edmund