I want to put a word in here for being cautious about the capabilities you can achieve in novel systems --- software developers are often working with multiple whole sieverts of novelty without realizing it --- without having a lot of the boring theory stuff nailed down.

If you're using (say) libsodium to do exactly the kind of thing 100 other developers have successfully used libsodium to do in the past, you're fine. But it takes a deceptively small and subtle set of steps to end up synthesizing a new cryptosystem (see: attempts to build secure messaging systems out of libsodium primitives) without realizing that's what you're doing.

Learn a bunch of the theory! It's important.