Agreed about the carrier liability (or lack of) — I’ll often book multiple carriers to save money, so it’s one of the reasons I make sure my travel insurance covers delays, missed connections, etc.

Be aware, however, that buying separate tickets for a multi-leg trip (as the Boston > Berlin trip is described in “Alternate Routes”) carries a risk: if the first flight is delayed or canceled, and you miss the second flight, the second airline will consider you a no-show. Neither airline will have any responsibility to take care of you, or provide you with lodging or transportation to your destination — you’ll be wholly on your own.

Travelers should assess their risk tolerance. If the transit connection is short, or the earlier leg is frequently late, another choice of route or timing (or buying both legs from a single airline so the flights appear on the same ticket) might be superior.