The analogy proceeds thusly: sometimes (fairly frequently, these days) it runs out of fuel or has some kind of critical failure. Its operator is smart as hell but not especially reliable, and may be prone to taking unexpected directions or needing downtime at inconvenient moments. It has significant problems in several major systems and there is no part of it that hasn't seen better days. But its kludgy re-routings get the job done, to a degree that's really kind of impressive once you know how much of them is made of creatively applied duct tape. It is, against all odds, still flying.
Also, somebody keeps having sex in the engine room.