Page 25 - Peter Randall "The Craft of the Knot.."

Besides being the foundation of many different knots, the Overhand
Knot has many distinct properties of its own. For example, it weakens
most cordage it is tied in by 50 percent or more, and tightening it down
can damage the fibers of some ropes. Consequently, it is tied in nylon
fishing line to test for brittleness. If fishing line has lost any of its
flexibility, it will break very easily as you tie an Overhand Knot in it and
tighten it with a quick jerk from both sides. Fishermen take care not to

accidentally let an Overhand Knot form in their line so as not to lose half
its strength. Once it’s tied, the knot is difficult to undo. It should only be
tied in small cordage or thread if it is not meant to be untied.

THE FIGURE EIGHT SERIES

The figure eight series contains frequently used knots. This series begins
by making the crossing turn that would be used for an Overhand Knot,
and then increasing the number of times the running end is wrapped
around the standing part before passing once through the loop. Twisting
this loop an increasing number of times before threading accomplishes
the same thing. This series of knots is often used to stop a line from

passing through an opening.

FIGURE EIGHT KNOT

This knot is started like the Overhand Knot, but here the running end
makes a complete round turn around the standing part before passing

through its loop.

STEP 1 Use the running end to make a crossing turn, and pass the end
under the standing part.