These are the mistakes traders make actually. I wouldn't even start my position with more than 20% of my total portfolio because I cannot lose them all. However, some people invest their 100% portfolio and even take loans to increase their position size. This is a dumb decision, to be honest. No trading is 100% safe. So, how do people actually take the risk to invest their 100% portfolio in a single trade?
A trader should invest 10% of his portfolio in a trade. In case he loses one, he could recover that loss with his remaining 90% portfolio. There is a possibility of losing trade multiple times in a row. Considering this, they should not open a position with more than 10% of their portfolio.