Blue note, as many other sound combinations, is very sticky and a beginer piano player once it learns it, can not stop playing it. But blue note is a new invent, it didnt exist in the eighteen century for example. So why is it so sticky if it doesnt seem to come from the ancient world (it doesnt seem to be a genetic friendly sound).
To explain what blue note is i can give you an example, If you play C Major in the piano (that is, the combination of Do, Mi and Sol) and then play Sol flat (equivalently Fa sharp in the piano) you are playing the blue note. That note presents a clear disonance with the rest of notes (that is, its fundamental and overtone do not coincide with the ones of the other notes) and feels very nice to the ear. That is blue note.
You can't actually play the blue note on a piano... It's between the keys.
So, how does one play a blue note on the piano then?