What does it mean?

The plane flew over him just after he passed Jim Rennie’s Used Cars, a place for which Barbie had no love. Not that he’d bought a lemon there (he hadn’t owned a car in over a year, had sold the last one in Punta Gorda, Florida). It was just that Jim Rennie Jr. had been one of the fellows that night in Dipper’s parking lot. A frat boy with something to prove, and what he could not prove alone he would prove as part of a group. That was the way the Jim Juniors of the world did business, in Barbie’s experience.

Hi. Does the underlined part mean "when it comes to certain things that he could not prove alone, he would prove them as part of a group instead"?

Thank you.