One full market cycle of either Bull-Bear-Bull or Bear-Bull-Bear; if you are lucky enough you may encounter this full market cycle in less than 10 years or unlucky more than 10 year or 20 years.
That is why investing is tough!
Read? Wise Words Series - Part 3
Stock picking is part science, part art, part luck, part intuition, and always uncertain - "not precisely knowing." (Who say it? Forgotten)
or you just go for index investing which is easier as there is no stock picking!