Over-leveraging kills: True?

That's true but if your position size is too big for your account, your stop loss will be too small and it will tend to get hit quite often which will slowly blow up your account.

The life/death of a trader depends on the expectancy of his/her system rather than leverage.

Leverage is just a tool to get you the capital you don't have to hold a larger position size.

Naturally, the larger the position size the greater the average gain/loss for each trade.

Expectancy = (Average Gain * Probability of Gain) – (Average Loss * Probability of Loss)

However, if you have a hugely positive expectancy, what is to stop you from trading larger?

Expectancy is an average value so try not to blow up your account on the first few trades by risking too much.

I second other users comments on effective leverage and that leverage is merely a tool available to traders from their brokers; in order to trade with increased capital but within the agreed margin based on their deposit e.g 500:1 100:1. How large the size of their position relative to their available leverage shows their utilisation of that leverage... and it plays into the issue of risk. Using larger positions relative to account size = Higher leverage Utilisation = Higher money managment account risk per trade (if using a fixed stop loss for example)

Stop losses are another sidepart, and are used at every traders discretion; there on traders on FF who swear by not using stop losses. I would note however stoplosses may not get activated at the desired price by the broker due to illiquidity and slippage during news releases and high volatility for example. Just ask all those EUR/CHF traders who used Alpari as their broker.

I would recommend looking at USD/CHF during the week of January 11th 2015.
Base position sizing as if on the wrong side of that move. What is the maximum pain willing to absorb?
I trade 1% risk on each position (which is low for FX) and still would have taken a 10% hit, had I been on the wrong side of that trade.