For the mathematicians out there, this assumes that you win or lose the same amount on each trade. That is unrealistic, but I'm just trying to explain the risk of ruin problem. The point is that in order to reduce the harm caused by unavoidable strings of losses, you must keep the amount you risk on each trade to about one or two percent of capital. This makes trading with small accounts difficult. Another element of risk is the market you trade.
Some markets are more volatile and more risky than others.
Some markets are comparatively tame. Some markets, such as currencies, have a greater chance of overnight gaps which increases risk. Some markets have lower liquidity and poorer fills which increases risk. Don't feel you have to trade any market that might make a move. Emphasize risk control over achieving big profits.