I see it as there are those who lack street smarts and in the world of the Sopranos and a lack of street smarts can get you hurt or worse. Matt, Sean, Jackie Jr. and his glorified crew, AJ, and even Chrissy at times expected to have things handed to them with minimal effort.

Matt, Sean, and Jackie Jr. had the aptitude to make it to college and even graduate (implied by Matt and Sean having Stock Broker's Licenses). However, they didn't have the street smarts or honestly patience to work their way up in the criminal world . They seemed to earn decently under Ralphie/Chrissy, but their impatience and ambition was their ultimate undoing, not necessarily a cognitive shortcoming.

This is reiterated in season 6 with AJ wanting to be the owner of a night club without any practical experience, but once he got sage advice from Tony, then he mellowed out and appreciated starting out small and working his way up. (Though I wish I could work my way up driving a measly BMW as an intern)

Some individuals are simply intelligent and resourceful, school or no school, Ralphie didn't even finish grade school, but he sure as hell was better than 9/10 of most Accountants. If it weren't for the thrill of crime, he could have been a legit business owner

Those who lacked significantly in both departments of street smarts and basic common sense:

- Some of Tony's mistresses, as according to his own words, "They don't have many thoughts" lol. You could say Irina, but I chalk that up to her being a "poor confused kid from an underdeveloped country"

- Georgie, just didn't know when to stop when talking to Tony or any of the guys. The fact that he was in the same cognitive league as Mama Soprano when it came to the telephone speaks volumes.

- Noah, Colombia or not, books don't save you from the potential wrath of an angry Dad who runs all crime in North Jersey, he was lucky he still had his kneecaps. Didn't he have any common sense not to get involved with a Crime Princess?

Ultimately, I'd have to say Jackie Jr., he consistently antagonized Tony by getting involved in the "business", hurt Meadow (via cheating), failed out of Rutgers, and seriously underestimated the ramifications of taking down a card game of a Made Guy, then attempting to clip two of them to boot. It is almost a suicide by cop stunt Jackie pulled in the street world and civilian world to get the prize of being "Made". Also....he almost drowned in the Penguin Exhibition....