Is programming MK, ASM really 30-40% more efficient than C?

Question

Microcontrollers

Hello!
I am reading a book on programming microcontrollers, the author writes that firmware in C is 30-40% less efficient than in Assembler.
Tell me, is it really true?
Simply, C is much easier and I know it basicly, and Assembler is completely incomprehensible, you will have to strain your brains a lot to master it, if this is really the case.
That is, without options to learn Assembler if I want to become a good Embedded Engineer, or can I do with C?
Thank you!

Answer 1

Tell me, is it really true?

On the contrary, modern compilers make similar (without micro-optimizations) C code more efficient.
You will write in C and some other languages.

and Assembler is completely incomprehensible, you have to strain your brains a lot to master it

It will have to be mastered anyway.
For understanding how things work and for debugging or learning.

That is, without options to learn Assembler if I want to become a good Embedded Engineer, or can I do with C?

Can't do without C.

Answer 2

Once upon a time I bought a book "writing drivers in assembler". There were examples for Windows3. As soon as I got to Windows NT, the author wrote: "further we will write drivers in C". The question is, why such a title?