We decided that certain things are pretty much only going to feature in the news for a short period before they come back to life again - Strictly, X-Factor, I'm A Celeb etc.
While they are running they feature heavily but once over, barely get a mention so as an extra "dynamic" for the website they are given a life span - after that time has been reached the stock instantly becomes worthless.
So, the challenge for you is how long are you going to keep your stock? If you hold onto it for too long and the magic date passes you'll suddenly find it's worth nothing so you'll need to balance how much you want to make against leaving it to the very last minute before selling.
Of course we are all open and up front about this so when you buy a stock with a life span attached, you'll get a warning to tell you that after a certain date it will be worthless.