For me personally, its all based on the number of times I've been burned.
Bio is very unpredictable, even with good data. Too many times I've waited for the market to reacted based on commonsense (the thought of it is even funny). Sooo the approach that works best for me now is a 60/40 Core/Trade.
I sold 3841 shares today in preparation for Monday selloff and held 6229 in my core.
Long story short, people who want to stay long are a little nervous (going into the weekend). And new investors who are doing their DD are coming across articles and tweets outlining the fact that AVXL only has 32 participants.
So I understand why we are only at 4.35 ... just my 2cents as a non technical (YMB flunky) investors who stays in the background.