I can darn socks. And there are bunches of online tutorials. Knitters who have spent tens of hours making a pair of socks do not consign them to the rag bin for a small hole.
video: http://www.knitpicks.com/tutorials/Sock_Darning-Swiss_Darning_part_1__D171.html (There are more videos to that tutorial, but that's the start.)
different text: http://www.hjsstudio.com/darn.html

When I darn commercial socks, I use sewing thread or embroidery floss.

I'd be so sad if I lost my stripy kneesocks because of a hole.