English-language comments are usually full of prepositions, ambiguous terms and mostly stuff that was meaningful just to the author. Words about data in our out, upstream or downstream are always useless because nobody else has any idea what point of view you're taking (data produced BY your code, or produced FOR your code?)

If you think you're making things clear to somebody coming after you, I'd guess you're wrong most of the time.

And then, the code changes but the comment doesn't. Now its downright misleading.

Also it's arrogant to imagine somebody who writes good code can also write good prose. Testing shows most folks are good at one or the other, right? Math or English, few can do both.