1) trading too big for account size & knowledge IE not managing risk 2) mistaking high probability for certainty
1) Not having/executing a sound trading plan with adequate capital 2) Not exiting a trade at a pre-determined risk level (stop)
what are the two worst things a trader can do? Start trading and blow a 2nd account. Yes and no. The actual signal involves an expectation but from that point on there should be no expectation or prediction as to what the market will do, otherwise you have a flawed and non-optimal exit strategy.
what are the two worst things a trader can do? Going after tiny gains - you need real big winners to make it in this game. Over trading - this is given as a primary reason in most studies as a leading culprit for failure.
Your underlying spikes down and your stopped out, then recovers immediately missing the bounce, only to shoot upward to big profits and ex-dividend the next day. Ok that's more than 2. And that is why stop loss is going away.