I would play in minor keys for the beginning of the piece and major keys in the latter; at some points I would play minor keys. My life is like a roller coaster regarding happiness or lack of happiness. Sometimes I am happy in life and other times I have to deal with difficult situations. Of course, I am not happy with difficult situations, therefore, minor keys are a sufficent choice during these times. Contrastly, I have happy life periods so that major keys are proper to be played in the piece of music.