My first solo trip was 20+ years in the making.
Back in the mid 70's, 3 other guys and myself started doing backpack trips.
2 of us lived in MI and the others in Atlanta and Boston.
We took turns planning the trips, but increasingly I ended up doing the detail work even on others trips and being the driving force behind them.

I was into the work-out thing and still am, but they were 3 guys who liked to party.
As we aged they became less able to handle the physical demands of a backpack trip and so we got into canoeing at my suggestion. I figured even with portaging, it was easier than a 15-20 miles a day with a pack.

Worked for awhile, but there was a fatal flaw in my plan. You can bring more gear paddling.
In their case that meant more booze and other recreational products.
Soon the trips became party around the campfire until past midnight, sleep till 10 am, get on the water bitchin all the while by noon, and then want to stop by 3 PM, sleep till dark and then repeat the cycle for the length of the trip.

Meanwhile I was doing all the navigating, wood collecting. fish catching/cleaning and 1/2 the cooking.
At the end of the trip I was mad as hell and promised never again. They would give me a few months to calm down and then start up about the next trip, promising they would be better this time.

I blame myself for allowing them to manipulate me but I'm a loyal type person and we had known each other for a long time. I allowed that to overrule my common sense.

Straw that broke the camels back was the year it was my turn to plan the trip. We had 10 days to go down to Jean Lake and back out at Beaverhouse. Ended up going out thru Sue Falls and taking that time to go 25 miles. I was beyond pissed off.

I had a big fight with them and 2 of the guys said they were done with me becasue I wanted to "work", while they wanted to party. The last guy and I went on a few tandem trips, but he eventually decided he rather party too.

My first solo came when he backed out 2 days before trip. I ended up going alone and even though I had some mis-adventures and didn't go very far, I realized that the only difference for me in going in a group ( at least that one) and going solo was I didn't have to listen to anyone whine and could enjoy the serenity without having to herd the Tom cats toward the take-out and being the object of their bitching when problems arose.

I could see doing a group solo or with the right people a group tandem trip, but before I would sign on for either I would want to set the ground rules beforehand and make sure are goals/wants are the same.

I agree with the introvert/extrovert thing. If you can't stand to be alone with your thoughts, then solo isn't for you.

During the day your busy and it isn't much of an issue, but at night around that campfire you really come to understand your on your own and responsible for your decisions, good or bad. Some people find that more frightening than anything.