QT....there is no rigid rule that I use. I said generally when I am up 50% I take half off the table. If I analyze the situation and see that momentum is still strong and gaining strength I will wait. BUT, I have seen stocks drop so fast that you are lucky to get out at a break even level once they start dropping.
I don't have any problem with your logic but my logic is not flawed either. Profit is profit. I would rather be assured a 50% (or better) gain than to have seen that 50% gain on paper only to watch it disappear when a stock begins to drop and end up with next to nothing.
This stock could start downticking in the premarket on Monday and by the time anyone could get a sell in it could already be down 20 or 30 percent. Now, I am in NO WAY saying that is going to happen but I HAVE seen it happen. Once again, I get back to profits are profits.
There is an old proverb written by an ex penny stock trader that is now a millionaire and he said " I guess the reason I made so much money is because I always sold to early". That is sage advice IMO.