According to the Gambler's Ruin, using your trading account as a source of income is a statistical insured bankruptcy. I can recommend you to watch this Harvard lecture for a detailed explanation of the statistical calculations.
In summary, to avoid bankruptcy the capital must not be allowed to decrease. Because, for every decline in capital, it becomes easier to go bankrupt and harder to make a profit.
If you are culling your trading account by withdrawing capital on a monthly basis. You are in practice adding up perpetual losses in the form and magnitude of those withdrawals, decreasing the account and moving you closer to bankruptcy.
Trading has only one purpose, it is for the purpose of growing your account. Of course, when a trade is done, I recommend you to use a small portion of the profits in order to enjoy the fruits of your efforts.