Is learning C really a must for a programmer?

Many have this opinion. Somehow, by doing manual memory management allocation and garbage mangement one would become a better programmer.

I have little experience in C mainly because I can write terser and more readable code in Racket or Haskell. However I'm willing to give C a try just to learn these lessons that everybody keeps talking.

But I have a sneaking suspicion that I already know most of what is there to know. Can you list some useful lessons that a typical high level code dweller would be oblivious of?

Manual memory management doesn't make you a better coder though
It does. By forcing you to think about how much memory you use, and explicitly allocate/free, it gives you better understanding to reason about how you should use memory. You're less likely to do stupid things like making copies of data that weren't needed, or keep around memory that should be freed.

It's easy to see this in code written by ex-Java programmers who have migrated to C++. Object copies and new everywhere.