Lao-tzu on literature reviews:

Thirty spokes share the wheel’s hub,
It is the centre hole that makes it useful.
Shape clay into a vessel,
It is the space within that makes it useful.
Cut doors and windows for a room,
It is the holes which make it useful.
Therefore profit comes from what is there,
Usefulness from what is not there.

Okay, so it may not have been intended specifically for lit reviews, but it's still worth keeping in mind...