My 80 year old mother plays in F. When she was carrying me, no doubt she played in F. She taught me the F chord, the B flat chord, and the C chord. Then she showed me the first and second inversions of those chords. I had a harmonic reperitory of nine chords to harmonize a melody. She explained that the F chord was the home chord, around which all the other chords revolve, but eventually they must come home to F. This is how I learned what a key was.
Naturally F was my first and favorite key. I could hear the chord progressions easily in F.
I quickly had to learn C and G to give some variety to my playing. That's when I discovered secondary dominants. So I learned how to modulate between they keys of F, C and G quickly.
I soon learned that people in churches get up and sing everywhere. Some singers stay in the key they start in. Those you can always play melody for and chord out some kind of harmony. However some singers are all over the place when there is no modulation. I lay out when I hear this kind of singing. They are doing their thing. They don't know what they are doing, and they don't know where they are going. Naturally I can't read their mind or guess what unpredictable note they might sing next, in this kind of situation.
Over the years I have learned how to play in all twelve keys. When I first became a member of this august musical community, I was having trouble hearing and feeling harmony and melody in F#/Gb and B. After having to take an early retirement do to a lack of music teaching jobs here in Michigan. I can safely say that I am now comfortable in B as well as F#/Gb. Long periods of time on my hands helped me to be a better musician. When I was working I didn't have the time to put in on my instrument. Knowing what to do intellectually, is not the same as actually applying the knowledge to the instrument where it becomes spontaneous.
brother scott