How is it different from a square knot?
If you look at the ASCII representation of the knot below, you will notice that the running ends, A and B, end up on opposite “sides” of the tied knot (in this illustration, the top and bottom). In a square knot they are both on the same “side” (i.e., both on the top or both on the bottom). Because of this difference, the thief knot will slip when under stong tension, and should never be used when safety is at stake.
