This is a valuable lesson, 10BTC too expensive, many people will be stressed. You are right, we need to determine exactly how much we can lose, it is very important to help us not lose confidence in our investment plans.
Ten is just a number is it not? For some people 10BTC is nothing but for some other people a double digit bitcoin figure is a big deal.
Of course I dont believe that the person lost 10BTC completely without having bought something because it is a trading and if Spot trading they definitely bought some altcoin with it. If they went for margin trading on the futures market like bitmex then it is a type of gambling but possible to lose the complete capital.
Now it is stupid to trust a "influencer" on social media. People who trust them are fools in the first place and thus I would question how they acquired 10BTC in the first place? Still it does not make it any good and people should do their own research for trading.
Critical!! You don't lost your capital when you trade, it's just another sense of inefficient trading. You choose to trade BTC with another coin that doesn't have enough potential to bring you expected profit. However, you just "trade", you don't "throw" anything. You trade BTC with another coin, that's what you have. In the other hand, if you choose gambling like margin trading such as Bitmex. That's your call, some people are still too fool to know that gambling can't bring you profits in the long-term way.