> You never understand other people's code as well as your own. No matter how thoroughly you've read it, you've only read it, not written it. There is certainly some truth to this. On the other hand, it's possible to become blinded to defects in code you've written yourself. You see what you intended for the code to do rather than what it actually does. Reading someone else's code, it can be easier to see what's real…
Then a review becomes something like "the claim was made this function does this, does it look like the function does what it says it does?" If you can understand it in context, then you've added trust and knowledge of how it works.
However it seems to often be the case a review turns into "I like this word better than that word" so back to the explaining it point, it becomes a bit of a self review with the hope it might be helpful to somebody else in the future.