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?

>>4
It's easy to see this in code written by ex-Java programmers who have migrated to C++. Object copies and new everywhere.
Aren't ex-Java programmers more likely to pass pointers by value, since it's roughly equivalent to a Java reference?