how come humans have not found out about the whole ocean

Question: how come humans have not found out about the whole ocean
- Keywords:
  earth,
  water,
  world
Asked by scientist Emmett to Maureen on 6 Nov 2018.
- Maureen answered on 6 Nov 2018:
  
  It’s really hard (and expensive) to explore the ocean! However, it means that there are lots of exciting things still to be discovered! Hopefully you can help us out with that in the future. 🙂 The R/V Celtic Explorer [https://www.youtube.com/watch?v=WLMC3mxnvQk] helps us with that.

Question: how come humans have not found out about the whole ocean