When it comes to learning to play an instrument, a reason why people tend to seek teachers is because there are several barriers that teachers help to break down. For example, you usually need short, easier songs to start with, so you can work your way up to the harder, more interesting songs, but simple songs (real simple, like I'm talking straight infantile) are usually more boring, thus less popular, and thus harder to find. Teachers help with this because over time they acquire tons of dead easy songs, hard songs, and the whole gradient between. Also, teachers provide a shortcut to valuable knowledge, like "the more you do it, the better you get" or "start simple and work your way up" or "remember to take breaks". In short, teachers are like grocery stores. Sure, you could go farm-to-farm trying to get what you need, but it's much easier to go to one source that is experienced in getting you what you need. Rebuttal?
in my experience, the teacher student connection has never been strong enough for any of the good/important stuff to make the transfer. this is reconfirmed again and again every time i hear someone say "i used to do music, i took lessons and i hated it and quit." added to all the great players out there who are self taught. advice can surely be transfered from one person to another, but it seems it mostly works on a non-teacher basis, not scheduled. for example you find a player you really really like and you check out all their stuff. or maybe there is someone you trust and you can ask them questions about certain things. i don't know if that counts as teaching but that works really well and i try to make that happen on the questions page as much as possible. although sometimes, my best answer is not something they are ready to hear at the time, or maybe they just aren't interested in doing the same way as me, which is ok, but it would get very awkward if someone was paying for us to have required meetings each week and pretend we were getting somewhere