Ugh! I've had to deal with this in a situation where we needed two sensors to tell if an object was present or not, but there was only space for one. So we coul

Ugh! I've had to deal with this in a situation where we needed two sensors to tell if an object was present or not, but there was only space for one. So we could tell if the payload was not present, but not if it was. This meant that we would have to make assumptions like "you (other subsystem) say you had the payload and you gave it to me, and I believe you, but I can't prove that you did until much later in time." And if it turns out that we weren't actually holding it, then recovering from that state required unwinding a whole series of decisions and actions made some time in the recent past. Suffice to say, it made error handling for certain cases... challenging!