That's a bloody joke.

Define 'learn' - to what depths? Learn databases next to grep/sed etc. Cringe.

All the trendy crap you likely won't need: mongo/influx/firebase/cassandra/redis - learn it if you need to. Hopefully some of these will be untrendy pretty soon, then forgotten.

This is bad and it's not credible to learn all this to a useful level. This is laughable. I hope starters here aren't put off by this.