An interesting corollary of the efficient market hypothesis is that, neglecting overhead due to things like brokerage fees and assuming trades are not large enough to move the market, it should be just as difficult to lose money trading securities as it is to make money.
No, not really. In an efficient marked risks uncorrelated with those of other securities shouldn't be compensated, so you should easily be able to screw yourself over by not diversifying.
Here's the new thread for posting quotes, with the usual rules: