Speaking in an interview with Guitar Center, Dream Theater’s guitar master John Petrucci revealed the “cool thing” about picking E Minor. He said:

“Now, the cool thing about picking E minor is that all of the open string are in the key. E, B, G, D, A, E, all those notes are in the key of E minor so you can use really any one of those to do licks or enhance chords in this key.

The first thing, you need to learn the scale on one string and then use the open high E to create this kinda two-note chords that are gonna enhance your melodic playing. So the string we need to learn is the B string, and you can start on open B and play all the notes in E minor.

And then what you have to keep in mind is that the high E string is going to be ringing out as you play those notes. This sounds really good with distortion. It’s gonna create sort of cool two-note chords. And the idea is that you hit the note on the B string first and then you play the open E and let it ring. With some of these notes it’s gonna be a little dissonant, with some it’s gonna have a little more harmony, some it’s going to be unison when you play it.

I think that because there’s distortion, because there’s a little bit of dissonance in your sound, you can use it to build a solo. You can even do something as simple as the solo is building and you climb up the scale with that high E ringing. It’s a really simple yet effective way of adding some excitement to your playing.”

You can watch the entire interview from below.