Don't get me wrong it is possible to teach yourself but takes alot more work and extreme amounts of struggling and dedication, however I did it and know others that did it and it is definitley possible.
If you want to teach yourself you still must learn theory anyone of marginally good playing understands theory.
Heres a few steps when teaching yourself(they are not in any particular order)
1) Buy Begining asoustic guitar(it is applicable to electric as well and is a great tool) By Greg Horne. There are three of them after 4-6 months get the next and so on.
2) Get a metronome- Practice the exercises within the book while keeping a rythm by utilizing a metronome.
3) Study music styles and find out what you want to learn
4) Learn easy songs that you like and try to cover them learn the vocal melodies
5) Learn the intervals-they are the building blocks of music and very important
6) Learn the major scale and all its positions
7) Learn how to read tab, dont waste your time with standard notation (thats my opinion).
8) Try to get another guitar player to practice with and try doing blues progressions, trade-offs, alternate on solo-ing...etc..
9) As you practice your scales sing the notes it will improve your relative pitch
10) Practice regularly like 2 sessions of 1 hour a day if you can. I feel the more the merrier however make sure its structured time
11) keep a journal
12) Learn the CAGED theory
13) Practice doing chord speed drills- Take a dozen chords and practice alternating between them as you learn new ones add them to the list.
This will take a while to learn all this however it will let you see if you have the ability, time, and patience to teach yourself. If this fails get lessons, I think most self taught people wish they could go back and take lessons, you will undoubtedly be better with them. However I have gotten pretty decent on my own and am proud of that!
Good luck,
Thomyorke575