If All You Have Is a Database, Everything Looks Like a Nail
I think> "Isolate applications.  Keep different applications away from other applications’ tables."is only good advice if the tables are application specific data and you don't do microservices in that stupid braindead way that makes it so that everything from the admin panel to data visualization are their own "applications" with their own databases and doing things that would be even the simplest of queries becomes a project in writing what are effectively bad performance joins via random http APIs. IE have a data model and understand where the most painless boundaries are, don't throw up dozens of DBs for the hell of it.