SCRATCH THE SURFACE: what does that mean?

One of these days I watched a lecture on a somehow complex theme and right after the end I had the chance to talk about it with a friend of mine who happened to be there watching the same lecture. I was curious to know what was his thoughts on what he had just heard and whether or not that was a good lecture to him.

He was pretty straightforward in his answer: I don't think the lecturer did a good job at all. Actually he barely SCRATCHED THE SURFACE!

scratch the surface

if you scratch the surface of a subject or a problem, you only discover or deal with a very small part of it

Another example I can think of happened just now while I was watching a movie (actually that was what encouraged me to write this post). Three girls were on a conference call and they were talking about this guy at school they considered a Greek god. One of them went as far as saying something like "I could write a thousand songs about him and I'd just be scratching the surface". In other words, that guy was so beyond words she could barely express how awesome he is in a thousand songs. That's a lot, right? Give your own examples down below in the comment section. Talk to you next time!