When is it better to just scale up a single database instance rather than sharding?

Our data storage keeps growing, and sharding our main relational database has come up. I'm wondering if we're maybe overthinking this. When do you all decide that just getting a bigger, more powerful database (vertical scaling) is actually better and way simpler than sharding? Are there certain points, like how many transactions we're doing or how big our data is, where dealing with sharding just isn't worth it compared to a beefier single server? Or does it really depend more on how we're actually using and accessing the data? I'd love to hear about your real-world experiences or any rules of thumb you use for this kind of decision.