it's the same as it is in anything, in science in art, when you do it by yourself you get comfortable doing the same thing over and over again, unless there is some sort of competition or wanting to outdo, or impress or just get new it's really hard to innovate by yourself. I know when our crew used to be like 12 people i came up with new shit almost every day now that I ride alone it's much harder to come by or to push myself to learn the new thing i'm trying simply cuz noone is there to try to learn/do it for. riding with other riders definitely helps everyone out involved push themselves.
