GREAT QUESTION! Actually, its funny because a lot of guitar teachers try to make you master something before moving on to something else... and that's sort of like learning how to add and subtract before you learn to multiply or divide.

It works for math, but... not guitar playing. That's because math is a science, and guitar playing is an art! You can write songs even before you know any chords, or how to play any other songs. They may not be the greatest hit songs, but you can still do it and have fun with it. :)