scratch the surface
US /skrætʃ ðə ˈsɜːrfɪs/
UK /skrætʃ ðə ˈsɜːrfɪs/
1.
to deal with only a very small part of a subject or problem
:
•
We've only begun to scratch the surface of this complex issue.
•
There's so much more to learn; we've barely scratched the surface.