Even if you could learn on your own and not develop incorrect habits/techniques, you still would not be skilled in fighting at all. you would not have developed a sense of proper distance, that comes from working out with a training/sparring partner. Fighting with friends does not work because you don't know what you are doing wrong without a coach to watch and correct what you are doing. you also can't develop a sense of timing without sparring with someone.
Bottom line is you need a good coach and one or more sparring partners in order to learn correctly. Otherwise, you are only mimicking moves and have no working knowledge of what it is like to actually use them.
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The better the teacher is the better you can be.Trying to be self taught is asking for a lot of problems.You won't even know if the things your doing are right or wrong.About not going to a gym your not in a Rocky movie.Try to find the best trainer you can.Good Luck
Slightly more difficult? Try near to impossible. You need someone to correct the many mistakes you will make and to help build on top of those corrected mistakes. You'd be lucky to even become an ametuer, which I am willing to bet is practically impossible.
you could learn the basics and maybe your stance and shadow boxing
if you learns by yourself correctly then when it's time to go to a gym to train you might have the upper hand in some sparring and fights and especially the training
Is it possible for one to become a professional boxer being only self taught? i could imagine it be slightly more difficult but just want to know if it is in fact possible to do? and also how wpuld one get started with that approach without joining a gym or anything?