Developer convenience is not a substitute for sitting down and learning SQL - but a good number of people I've met over the years plugging MongoDB et el have at some point thrown their arms in the air at the prospect of doing that.

Here's the thing, in practice relational databases aren't hard, nor will most devs ever need to know what relational theory is in order to be productive with databases built on it. Performance optimization does get a bit harder but there are relatively few situations where there's any magic involved, knowing how to read an explain plan and when/where to add an index is what most of it boils down to.