When an insider is dumping $2.5 billion (that's with a B) then you probably want to be concerned. Because, if GOOG valuation was so reasonable with expected growth, margin expansion or any other catalyst on the horizon, why would ES dump so much? If he wanted to simply diversify, he could have a much smaller portion sold now and wait for the additional appreciation on the rest before dumping a little more. This looks pretty alarming - 42% of entire GOOG stock is being dumped. That's a statement.