Though meant to be comedy, this video by "Axis of Awesome" is really one of the most important lessons to understanding the nature of Playing By Ear. The idea that one chord progression can be used with many songs is only part of the equation. In reality, any progression has the capability to apply to millions - even billions - or trillions of songs.
In the end, an underlying chord progression is just a formula that is devoid of any particular melody. Take heed my friends. An even more popular progression is a basic 1-4-5 Rock & Roll / Blues pattern. This gives one pause to consider just how close you are to playing by ear if you adopt this common sense approach to music.
Please leave a comment below and and share your thoughts about how important this understanding is to you.