Zandel is right about the math; for anyone curious about probability calculations, it goes like this:
The overall probability of an independent event over a number of trials is equal to A^B where A is the probability of the event and B is the number of trials.
The chance of rolling a 3* once is 63.5%. Over 11 rolls, the overall probability of getting -only- 3* is: .635^11 which gives 0.68%. It is indeed rare, though it is still more likely to roll all 3* than it is to separately roll a single 6*.
The chance of rolling what we typically refer to as salt though, consisting of only 3-4* is MUCH higher: the chance of rolling a 3-4* once is 93.5% and over 11 rolls, the overall chance of rolling nothing but 3-4* is .935^11 = 48%; almost a 1 in 2 chance of wasting 50FGs.
The overall odds of pulling a single 6* in a 50FG pull? 1-(.995^11) = 1-(.95) = 5%.