when does database sharding become a necessity

hey everyone, i've been thinking a lot about scaling strategies lately, especially as our user base grows. we're currently running a monolithic application with a single, albeit well-indexed, database. while it's performing well for now, i'm starting to consider what the tipping point is for needing to shard our primary data store. are there specific metrics you look at, like query latency, write throughput, or storage size, that signal it's time to move to sharding? or is it more about anticipating future growth? curious to hear your experiences and what factors led you to implement sharding