Example 1:

A trader has $4,000 worth of gold & silver and this trader only buys gold and silver for daily trading. Buy means price goes up. So Gold goes up 100% in 6 months

Now this trader has gold & silver worth $8,000 + $2,000 profit from daily trading. So the trader has $10,000 after 6 month.

Example 2:

A trader has $4,000 worth of gold & silver and this trader only sells gold and silver for daily trading. Sell means price falls. So Gold & silver price falls and after 6 months this trader has gold & silver worth $2000 + $2,000 profit from daily trading.

So this trader has $4,000 after 6 month.