yeah it can happen.  this is now a small pool. percent wise    down side means bad luck is really long and slow.  if you look at the chart 92% lasts 1 day.  there was a time a 92% block would take us under 4 hours .  why asic miner was king of the world last spring and came to our pool we had more then 30% of the entire network.  we made lots of 5 and 10 minute blocks.

This pool has a huge upside if it gets hot you can earn 3x what you should in a single day.     of course when you move here from a pool like btcguild or cex.io you can be very annoyed when the cold streak comes.  I finally got back to a high hash rate and am now at 850gh.  Was with the doc for more then 15 months in a row. but I moved to btcguild in jan of this year.

A few days ago I felt luck and switched back here hoping for good luck.  So my 850gh has earned me about .04btc in a 2.5 day period.
if I had stayed with btcguild I would have made around .24 btc  I was hoping to over earn.
not under earn with the switch.
  I think I will bail tonight as the bad luck is tough.