HOW? Dropped Stitch?

HOW in the world did I drop a stitch on these socks I am knitting.  I do not remember dropping a stitch, HOW? When I pick it up then I have one too many stitches, HOW did I add a stitch on these socks I am knitting? Good News they are just socks and one stitch that I will make disappear with knit two together will  be no big deal when it is on the foot in a boot.  Knitting can be forgiving.