> in trying to cling onto his success from the past he might have developed delusions that to him seem perfectly logical

Scary thing? Delusional behavior can just happen to anyone. It's a mental illness and like any illness there may be no way to see it coming. One day, you suddenly think your 'Real Girl' doll is a real person that you love[0].

[0]https://en.wikipedia.org/wiki/Lars_and_the_Real_Girl - Fantastic, true acting by an actor known mostly for his good looks.