Back in 1967, the US manned spaceflight program was grounded following the Apollo 1 fire. Not too long afterwards, the Soviet manned program was also grounded following the loss of Soyuz 1. Neither program launched humans again for over a year. Two completely unrelated accidents grounded both of the world's manned spaceflight systems. It wouldn't be very nice if such a thing left some astronauts stranded on the ISS.

Accidents sometimes run in strings. Back in late 1985, we lost a Titan 34 out of Vandenberg. Not too long afterwards, we lost the Challenger, a Delta, an Atlas, and another Titan 34. For several months, the only booster we had left operational was the Scout. None of these losses were related to one another except by how close they happened to one another.