Emagik77

Recently i've been trying to become a better musician by studying theory and practice practice pratice, but i have found myself not being able to really put any of the theory or things that i have learn into play during a real life practical musical situation. i understand theory a bit now but while im playing i find that know i think too much theory while i'm while playing. this never happened to me before i started to learn theory, i ran into a guy one day that told me that there is a Music Number System that most pros know but wont share with anyone or wont admit that this number system actually exist. Ive always been able to play by ear and i've always wondered why notes on an instruments where giving letter names CDEFGABC rather than number names 1234567-8 being octave, This guy told me that there are 12 notes on an instruments, and for each note there are specific chords that only goes with each specific note. while there are many chords and variations of them for each note he said that the music pros knows this but they wont say any thing about it being an actual theory for fear of a backlash. IS THIS TRUE? AND IF IT IS, WHERE CAN I LEARN THIS THEORY?