I am talking about the weakest form, and there has been many people who have done Ph.D thesis's on the subject and in the end the weak form is essentially true.
#2 a 19.99 commission is pennies on a 50k transaction, but then lets say you do 100 transactions a year, which I would expect is pretty minimal for a "day trader", then 19.99 x 100 = $1,999. Now that may seem insignificant as well until you start compounding 2k a year at 11% over 30 years... it's 5.6mil... not an insignificant amount...
of course if you are making money the whole time I suppose you can ignore that. but just how often are day traders right?
too many investors forget about fees and commissions, and lose REAL value over time.
I'd rather buy a SOLID company that is undervalued and hold it indefinitely... a company with solid management will grow value by either re-investing it's retained earnings or spinning them off as dividends, which can be used to purchase more of the stock...