Pretty much: Odds are that, if you roll your own, you’ll make mistakes which make your code trivial to break for a motivated attacker that is willing to put the effort into targeting you personally.

It’s also quite possible that the NSA/GCHQ/5-Eyes will notice that your communications are 'interesting, because different' and mark them to be stored in perpetuity in case they ever do decide that you’re of interest so that they can go back and break it all then.

So, how lucky are you feeling?