Right and as you point out that's not true. What gets less attention is why. I know in my own code there are dependencies I know very, very well. Some of them I have helped to author. Some of them I have helped with regarding maintenance programming later. But there are many which I don't.
There are a bunch of reasons for this:
1. Code has varying degrees of readability and is easily comprehensible to various extents. Code which reads like a book gets more time than that which I have to figure out its structure first.
2. Code that is well maintained provides less necessity to add someone else. I tend to be more likely to read poorly maintained code than well maintained code, for example because bugs don't get fixed is a good reason to try to fix them myself....
But this is anything but true. The reality is that code review is far less common than code use, with many defects impacting many users as the logical consequence.