Selling too early indeed.  While I have succumbed to such actions in the past, there is one instance that actually makes me smile.  I remember receiving my Nortel Networks spin0ff/distribution from BCE.  I promptly sold it a couple of weeks later for a 25% gain (hey, 25% in a couple of weeks is pretty good, I'll take the profits!).  

I then watched in dismay as it continued to rise to $120.  I mentally added up the "lost" profits, very  demoaralizing...until the collapse began eventually ending up around $0.19.

I certainly "sold early" however I avoided the collapse and can actually say that I made money on Nortel.

While stocks such as BMO should be fine as a long term hold, stocks such Valeant and Blackberry outline the fact that by selling early, you may miss out on some tremendous gains, however you will avoid being wiped out as well.