Just sticking to "I must comment each line" tends to lead to useless comments like
MOV X, Y ; Move X into Y

A comment that states what the computer does a result of an instruction is utterly worthless. If the 'reader' does not know what the computer does as a result of an instruction, that person has no business reading the code. A comment should reflect the programmers intent such as
;; the following istrructions average 8 reads of the ADC.

Line comments are often useful, but insisting on "comment each line" is ridiculous. My 'mantra' is "comment so the function of the program can be read without reading the instructions.

Erik