What i thought to be a cool company, turned out to be a shitshow.

Our "Team Lead" when assigning tasks keeps saying things like "it's only..." or "It's just..." or "You only need to change one line [there]..." And that's in regard to a terrible product with a pile of tech debt. So when you actually start to develop/fix things, you end up redoing third of the whole application.

How do you deal with this? How do you tell the "leader" that he should look into what we have in a code before making us all look bad for doing "just this one line change"?