I talk to myself a lot, and sing or hum. The talking helps me to jog my lousy memory, and to organize my thoughts. I live alone, so it doesn't bother anyone at home. When running errands I sometimes talk to myself about the errand, like what I am looking for in a store aisle, or that the door to the doctor's office is just a little farther (have bad knees and bad back, so this matters). As long as the outside talk is related to the errand, it isn't a problem. People usually understand that sort of talking to one's self, and it's not really that strange. Lots of people do it, because lots of people have so much going on in their lives, that they need this method to help organize their thoughts and jog their memories, so don't worry about it.
It's the other kind of talking to one's self that means something might be wrong. One time, at a place where I was staying, in the morning there was another guest outside having a violent argument with people who weren't there. It went on for a while. The people running the place realized that he wasn't playing with a full deck and arranged to have him stay at a facility for people with mental health issues, so he could get treatment.
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau