There is a widely cited (over 1400 cites in CiteseerX ) result called the Fischer-Lynch-Patterson 
theorem about consensus – a key issue in distributed databases or any system where data is either distributed or replicated or both.
In this paper, we show the surprising result that no completely asynchronous
consensus protocol can tolerate even a single unannounced process death. We do
not consider Byzantine failures, and we assume that the message system is reliable it
delivers all messages correctly and exactly once. Nevertheless, even with these
assumptions, the stopping of a single process at an inopportune time can cause any
distributed commit protocol to fail to reach agreement. Thus, this important
problem has no robust solution without further assumptions about the computing
environment or still greater restrictions on the kind of failures to be tolerated!
Crucial to our proof is that processing is completely asynchronous; that is, we
make no assumptions about the relative speeds of processes or about the delay
time in delivering a message. We also assume that processes do not have access to
synchronized clocks, so algorithms based on time-outs, for example, cannot be
used. (In particular, the solutions in [6] are not applicable.) Finally, we do not
postulate the ability to detect the death of a process, so it is impossible for one
process to tell whether another has died (stopped entirely) or is just running very
slowly.
The Wikipedia summary is similar:
In a fully asynchronous system there is no consensus solution that can tolerate one or more crash failures even when only requiring the non triviality property.[11] This result is sometimes called the FLP impossibility proof. The authors Michael J. Fischer, Nancy Lynch, and Mike Paterson were awarded a Dijkstra Prize for this significant work. The FLP result does not state that consensus can never be reached: merely that under the model’s assumptions, no algorithm can always reach consensus in bounded time. In practice it is highly unlikely to occur.
As far as I can tell the “surprising” result is that unbounded delays are not bounded. Without timeouts, we can not distinguish between a site B that will eventually send a message to site A and a site B that has failed (crashed) and will never send a message.