Reality is, I had a couple of instructors when I was a really new player (back in 1982!) and that did help get me feet wet in playing some stuff and knowing a few chords. My first teacher was really good but he left the store I went to and that was that. I looked elsewhere for an instructor and tried a couple. One of them, after my third lesson told me 'we are now going to teach you your style'. What? Heck, I'd been playing for a few months and he thought he could teach me my style? I thought that came with time...So, I kicked him to the curb and started off on my own
I got pretty good with no real help of instructors. What did often get was great advice from great players once in a while that was very useful. Otherwise, I figured out how to play to a pretty decent level on my own. It's possible.
Reason I'm at GT is that I never got the theory behind what I could play. To those around me, I played as if I knew my theory but that was my ear. As a player though, I knew my limitations were from not having a real understanding about how it all worked together. So, now that I am a hobby player, I come here to GT to learn those things I neglected.
Whether or not you need a teacher is all in how you best learn. I am a 'figure it out' kind of person and that's what I do for a living...Figure out complex problems to resolve so I'm good on my own. However, others work better with hands on direction.
So, depends on who you are and what you react to when trying to learn.