Why is it so important for you to know your keys in music?

Using the process of elimination.

Yes, there was a time when the internet didn't exist. I remember that time very well. In fact - for the first 36 years of my life, I managed to live my life without the internet. That means that in order for me, as an instrumentalist, to learn how to play songs on the guitar, I had to know a certain amount of music theory in order to understand basic st…