This is a lesson I wish I had learned earlier. Excessive leverage can ruin an otherwise profitable strategy.
Let's say I had a coin that when heads was hit, you would earn $2, but when tails was hit, you would lose $1. Would you flip that coin? My guess is absolutely you would flip that coin. You'd want to flip it over and over. When you have a 50/50 chance between making $2 or losing $1, it's a no-brainer opportunity that you'd accept.
Now let's say I have the same coin, but this time if heads is hit, you would triple your net worth; but when tails was hit, you would lose every possession you own. Would you flip that coin? My guess is you would not because one bad flip of the coin would ruin your life. Even though you have the exact same percentage advantage in this example as the example above, no one in their right mind would flip this coin.
The second example is how many Forex traders view their trading account. They go 'all-in' on one or two trades and end up losing their entire account. Even if their trades had an edge like our coin flipping example, it only takes one or two unlucky trades to wipe them out completely. This is how leverage can cause a winning strategy to lose money.