One of the most devastating mistakes any trader can make is risking too much of their capital on a single trade. One thing is certain in trading and that is if you lose all your capital you are out of the game. Why risk so much you could be prevented from continuing? There is a saying in
poker than going all-in (risking all your chips) works every time but once. This is true of trading.
If you risk all your account on every trade it only takes one loser to wipe you out (and no trading method is 100% accurate), so you will be out of the game at some point it is only a question of time.
In general, we only risk 1-3% of the available capital allocated to a system on any individual trade. This is calculated using the size and, the difference between our entry price and our maximum stop price, and the amount of capital allocated to the system. With the win probability and ratio of size of winning trades to losing trades we are almost certain never to lose all of our trading capital. In fact, the chance of us hitting our maximum drawdown for the year is tiny.
All trades should be of a size that almost seems insignificant. If you are worried about the size of a trade then it is too big and you should reduce the size immediately. Remember that longevity is the key to making money by trading slowly over a long time with minimal risk, is always preferable to rapidly with too much risk.