Structure that carries weight

A structure that consistently works: the specific moment or problem that pulled you into the field; what you did about it (a project, a job, a course, a failure); what you still cannot answer and want this course to teach you; why this department in particular — a named module, a lab, a professor's work; and what you intend to do with it.

Notice that four of the five parts are evidence. Only the last is ambition.