Indeed, and you cannot prove that a specific car crash would have been worse for the passengers without seatbelts, however a proper understanding of how seatbel

Indeed, and you cannot prove that a specific car crash would have been worse for the passengers without seatbelts, however a proper understanding of how seatbelts work makes the conclusion nonetheless fairly obvious. Also, statistics are a thing; propositions like 'vaccination reduces severity of illness' can in fact be proven or falsified by studying a sufficiently large cohort, such as is readily available during, say, a pandemic.