All very valid points to be observed by both beginner and experienced.
I would add that most often a loss can turn into a win. If you find you're wrong in a investment play the quicker you exit the quicker you can put that investment in another more optimal position. Take your losses...look at it as paying your dues.
Hey @cryptologyx I would agree completely with that if you mean that you are wrong in the fundamentals of the investment. For market swings I wouldn't recommend to exit if it goes for a downturn as long as the underlying value of the investment is still the same.