I believe it is rooted in legal proceedings where you are usually not required to in principle because it can be hard and/or impossible.

Eg. it is extremely hard to prove you "weren't there" (eg. at a crime site) if you cannot easily prove you were somewhere else (an affirmative): we do not keep court-admissible record of our whereabouts in case we get suspected of being in a place we were not in.

So it does hold in a number of cases where keeping evidence is required for proof. In software, that evidence would be formal specs and test reports which prove that cases covered with those are indeed working as specced, but provide no proof outside those "specs" (loosely considering an automated test a spec too).