Complex sentence: A fundamental result about distributed computing is that achieving consensus in asynchronous systems which suffer crash failures is impossible in the most general case, and can only be guaranteed in synchronous systems where there is an upper bound on message latency.
Split into simpler sentences: A fundamental result, about distributed computing is that achieving consensus in asynchronous systems which suffer crash failures is impossible in the most general case. Consensus can only be guaranteed in synchronous systems where there is an upper bound on message latency.