All people will change. Just like their appearance, their personality also will. I don’t believe that change is only a process that happens over long periods of time. We are very different people even at different parts of the same day. Look at your perspective before you go to sleep, and when you wake up. People set alarms at night expecting they are calling themselves to wake up the next morning. This generally fails, or at least doesn’t go according to the plan that has been set a few hours ago. This is simply because once you go into deep sleep, you would have just killed the man you were, and with waking up, someone new emerges. And that person will generally prefer to stay in bed for a few more minutes, or hours, unlike your predecessor who confidently set these alarms at night. As the day goes through, that new born personality will mature and by night time it would fall into the same mistake as its predecessor. It will always think that it will simply go to sleep and wake up again. But no, a personality lives for one day only where it matures and then dies once deep sleep is triggered. But every generation that appears every morning will recollect the cumulative experience acquired by its predecessors over time throughout the day.
Personalities do also radically change throughout the day sometimes. A man’s perspective on life and living could dramatically differ in the seconds separating between lust and satisfaction; people become entirely different under the influence of chemicals that vary from anti-depressants to psychedelic medicines, and man will also radically change in response to a radical change in their total assets.
Something though remains constant, and that is not the personality of man, but rather the cumulative experience that all these personalities have independently acquired. And it’s experience, not personality, that make a person who they are.