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?

>>6
Optimisation is never premature.

They just propagate that thought because they can use it as a defense against explaining having to spend more time rewriting/optimising what didn't work out the first time they wrote it, and thus earn more for doing less.