The bowline is one of the most useful knots you can know. Simple to tie, and easy to undo, the beauty of the bowline is that it creates a quick loop secured by a knot that tightens when under load. Sailors use the bowline to fasten halyards and other rigging which require a super-secure connection.
The one-handed bowline is a technique that allows you to tie the knot using only one hand. Why is that useful? Imagine you’ve slipped and fallen into a rushing river. At the last second, you grab the branch of a tree, but you can’t pull yourself up. A friend tosses you a rope to tie around yourself, but the only knots you can tie would require the use of both hands. With a one-handed bowline, you can secure a loop around your body while still holding onto the branch. In most scenarios this is a survival knot tied around your waist, but it can be adapted to a number of circumstances.