Some here may have opinions on why officer do or don't buy share, including me, however, we must keep in mind that SK, as far as I know, is not a wealthy guy (as in real wealth). He came from the lab and not some wealthy position. As we can see, he has to deal with everyday life such as wife, house, kids, education, jewelry, divorce, etc. Who knows how much extra cash he has or had to buy shares when he is already getting a ton of options.