Sending an email campaign to a few thousand people looks simple until the third recipient’s inbox provider rate-limits you mid-send, the fourth bounces permanently, and the process doing the sending gets killed by a deploy halfway through.

Memory is not a receipt. A landlord and a tenant agree a flat is fine at handover; six months later they remember it differently. A fleet manager hands over a van with a full tank and no dents; a week later, someone disputes which of those was true.