General things: when your session fails to migrate, when log compaction can&#x27;t keep up with writes, when logs fill up your disk (ZK used to require external cron jobs to prune logs), when watcher notifications arrive late, when the leader&#x27;s GC exceeds its heartbeat timeout, and so on.<p>Lots of things can and do go wrong with Zookeeper. I suspect it depends on the use case, but building a Zookeeper dependency into any system is potentially asking a lot of users&#x2F;operators.