The British psychoanalyst Donald Winnicott (1896-1971) said that it was rather an achievement to be able to think a) rather than b) or c). It doesn't come naturally; it requires years of good parenting. Winnicott observed that babies and small children whose mothers leave them for extended periods will give up hope that the mother still exists somewhere beyond their visual field. They imagine that she must be dead (or that she has found a better child to look after). In any case, they don't imagine that the mother has been held up in traffic or delayed at a meeting. They only develop this idea if her absences are minimal in the early years. As Winnicott puts it: "The feeling of the mother's existence lasts x minutes. If the mother is away more than x minutes, then her image fades. The baby is distressed, but this distress is soon mended if the mother returns in x + y minutes. But if she does not, then the baby becomes traumatised. In x + y + z minutes the mother's return does not mend the baby's altered state. Trauma implies that the baby has experienced a break in life's continuity..."
Winnicott stressed that the child's image of the mother is highly precarious and can suffer serious damage - a mother's 10-month trip overseas can seem like a death to her son or daughter. But adults who have not had traumas are able to develop a robust faith in the survival of others beyond their immediate surroundings. Someone's mother can depart for a year to Australia, but her image and memory will be capable of surviving the time and distance. She will not be killed in the imagination simply because she is absent - out of sight is no longer out of mind.
It isn't a conclusive explanation of why some people panic when there's been no phone call for a while and others shrug it off. But it does begin to shed light on the mechanisms of paranoia and anxiety. (M hadn't died, nor had she run off with Louis Theroux, her idol. She had been held up on a Circle line train between Gloucester Road and South Kensington.) Winnicott reminds us that, as ever in the psychoanalytic framework, we often worry in adulthood about things that went wrong in childhood. It's not to say that adulthood is free of trauma, just that we should beware of importing into scenarios where they don't belong pessimistic interpretations of others' behaviour.