i will use myself as an example, i have never taken a grappling class a day in my life; i learned by watching guys grapple and grappling alot. I have had people point out certain things to me, adjust what i am doing; but never in my life have i had a coach.
But i can in fact grapple, now am i very good, super technical or top shelf as a grappler; no im not, but am i functionally effective. Yeah...i have rolled alot w/very good wrestlers bjj guys judoka samboist shui jiao guys submission wrestlers etc. I got taken down, thrown, leg locked, heel hooked, armbarred, triangled, rear naked choked, etc. After being completely dominated for months and months and months; eventually i learned how to survive/defend, then improve position, then gain position, then maintain position and eventually submit guys. I didn't tap someone until seven months in; but that was rolling all three times a week against very experienced and skilled guys. An when i say i got handled..i mean handled..tapped out...worn out..beat the fuck up.
i been to multiple mma gyms...judo clubs....grappling clubs...bjj clubs and sambo clubs all over texas, and while noone is saying im great or very good...noone has said i don't know what im doing based off rolling w/me.
i can even point to specific moves i was never taught, just watched and then tried it until it worked... Sitting out, i actually saw bret hart do it in a wrestling match; he used it and i recognized i get in certain situations because of not knowing how to do this move. So i did again and again, in sparring; then i just figured it out and was able to pull it off...
So i have essentially taught myself to grapple...just talked about it alot...read it alot..watched people roll alot and sparred alot..and taught myself how to grapple.
Esp the style of grappling i used..it was all trial and error under duress rolling against competitive much better grapplers.
seriously never had anyone teach me how to grapple..maybe show me a diff way of doing a move here and there; other than that..watching and rolling.
That being said i am never gonna be a world champ..national champ...regional champ...state champ..etc. Im not good enough, i know enough and can perform well enough to be functionally effective..noting more or less... So do you need a trainer to learn, NO; but it depends on how good you want to be and what level your gonna compete at.
I believe you could teach yourself something to be eff in regards to self def, or to be better than other untrained/coached people; but unless your a exceptional physical/mental talent, you won't be high level in re to competition.
also if you have a base/prior teaching/coaching, u can pick up things and learn through trial and error; once again that is only gonna get you so far in regards to who u can be in w/and how well u can do vs them.
i learned how to parry and a baiting/potshot approach by sparring alot of karate/tma type guys; saamag taught me kickboxing/mt, but my approach in his opinion is more tma like as i apply what he showed me based on my prior experiences. The whole concept was based on alot of sparring w/alot of karate types; even though i never have learned karate, alot of people ask me if i have a karate/kung fu b/g because of things i do.
so i agree w/u based on my experience you can learn something from scratch or you can learn a new element/aspect of something through observation..trial and error. It just takes alot of time and patience and will; cus your gonna get smacked and embarrassed quite frequently.. At least i was.