And that's a dubious knot (esp. on relatively larger-diameter objects) which shouldn't see serious work!
Because the fully loaded strand puts its force on the
toggle part (the slip-bight) and can pull it through the "frame" it's toggled against. There is a simple variation to this carelessly published knot that avoids this problem : the fully loaded part will bear upon the frame, and the toggle will see much less force upon it.
Hmmm, Google("tumble hitch") and you'll find I think some various such improvements. This page's #29 makes an awkward, tuck-from-backside finish, but the simple direct tucking should be obvious :
www.southee.com/Knots/Knots_Hitches.htm
*kN* (darn curious to see if quoting works!)