Short ideas are harder to implement than longs, as you need to pay interests to maintain the position. On the other hand, market can stay wrong longer than you expect, causing both loss of the position and  shorting interest costs. Tilson’s story with WRLD shows how important a catalyst is for a short position. For influential active investors, if there is no catalyst, they can create one by publish some 100+ pages presentation (David Einhorn’s Green Mountain Coffee short, and Bill Ackman’s Herbalife, for example). For others, I think Tilson’s advices are very valuable: if you believe in your thesis about a short, start your position small and keep following the name, wait for a catelyst and you can double up.

URL: http://www.valuewalk.com/2015/09/world-acceptance-corp-is-going-to-zero-tilson/

What lessons did Tilson learn from this experience? Well, he notes that one takeaway from the experience is the fact that sleazy companies can keep doing sleazy things far longer than they should be able to, in part because it can take regulators many years to rein in even the most obvious “bad actors”.
“The implication of such lessons are clear: if you think you’ve found a great short in the mold of World, be patient. Size the initial position small, just to keep an eye on it, and then be prepared to pile in if regulators finally act.” — Whitney Tilson, Value Investor Insight