Breadcrumbing is structurally related to what attachment theory calls intermittent reinforcement: the behavioural dynamic in which irregular, unpredictable rewards produce stronger and more persistent pursuit than reliable ones. The person who receives breadcrumbs learns, over time, to organize their emotional life around the anticipation of the next one. The crumb itself becomes less important than the possibility of the crumb.
Most people who breadcrumb are not running a conscious campaign. They are people who enjoy being desired without wanting the full cost of relationship — and who have found, often without explicitly discovering, that minimal engagement is sufficient to maintain that enjoyment. What they are less aware of is what this minimal engagement is doing to the person on the other end: producing hope that is repeatedly almost satisfied and never quite, which is one of the most reliably maddening experiences available to the human nervous system.