Some people take knots seriously.
For instance, the Hercules knot, which is a simple, square knot, used to tie a rope around something... basically what knots do, when they're left alone to be doing what they're supposed to. But Hercules knot has an aesthetic dimension as well, unfortunately for it. It's symmetrical, and therefore caught the attention of jewelry makers and fashion designers since ancient times.
It's main use though is in medicine, to tie bandages. Pliny records that wounds heal faster when the bandage is protected by a Hercules knot, which, like many absurdities recorded by Pliny, is correct, and modern medicine still uses this knot to this day.
Another association is with Mercury, whose trademark caduceus displays two snakes which appear to form a square knot. This signifies the strength of an agreement (Mercury being the god of merchants, bankers, robbers, and other honest people) – the more the sides are pulled apart, the stronger the connection between them. By why do they call it Hercules knot, when it belongs to Mercury? Good question. Maybe the Gauls inspired the change, considering that they identified Mercury with Hercules. Or maybe not, I have no idea.
So – healing, commitment, bonding – the next logical step is to associate the Hercules knot with marriage, of course, and to use it for the design of bridal jewelry and clothing. (Hence the phrase to tie the knot? Hm. Maybe.)
The sad part is that the Hercules knot is actually very weak. The International Guild of Knot Tyers (told you some people were very serious about this) warns against its improper use, which allegedly caused many deaths over the years. Maybe you should think twice before selecting is as your wedding ring design. Maybe a Celtic knot would be more appropriate? How about no knot at all?