I've been just letting my holding sit, on the grounds that I...

I've been just letting my holding sit, on the grounds that I might eventually get some of my money back or if it goes under I haven't got much left to lose.
Recently, however, I read that if you're ninety percent down on a stock you should sell or buy more, don't just do nothing. Which leaves me none the wiser. I suppose I could double my holdings on the off-chance. Unfortunately it's an industry I have zero knowledge of, so no chance of making an informed decision.
Just thinking aloud really trying to clarify my thoughts.