You bring up some good points about whether or not to sell after this runup. Examine the numbers, decide whether or not PEGA will grow its top line into this multiple year over year, then go with your gut. Personally, I'm not selling because Trefler said this can be a $1 billion (revenue) company within several years. But do what suits your risk tolerance and smell test.
One thing I will pound the table on, though....is the word "greed". Nobody is the arbiter of greed. What may seem greedy to you is not greedy to others and vice versa. There are people who think George Soros is greedy. Likewise, there are people living in third world poverty who think you and I are already greedy, whether PEGA is at $100 per share or bankrupt. In short, not one person on this earth can sufficiently validate his personal determination of what's greedy and what's not.
The idea is to make money, to make the best investment decisions. If selling is one of those "best decisions", then do so. Same thing with holding. Congrats on taking the risk on this stock and being rewarded for that risk and for your own intelligent decisions, whether you sell or hold.