Of course it's hindsight. Actually the profits would be almost...

Of course it's hindsight. Actually the profits would be almost unlimited using your 'reasoning' ,instead in reality most traders don't make money. Also there have been studies that show the lazy investor often comes out in front. Share prices often don't make much sense in the short term. Tinkering or excessive trading can mean you miss out on growth stories as you will sell when you make a bit of a profit and buy something else when may or may not go up.

PS: I have a profit in DNK as I bought more when it went sub 20c and it's only 12% of my portfolio so it's not stopping me buying other stocks. Many others I hold aren't doing as well as my DNK though.