But saying that we should invest with an amount you can afford to lose makes it looks as if we are gambling or we are trading, this is an investment, no Investor will be happy losing his hard earned money, so in my own opinion, the right statement for such phrase is invest with an amount you can do away with for a very long period of time.
You are making the statement very complicated. Losing money does not mean that you are going to lose the money or that you will easily lose it. You can take this word to mean money that you will never need to meet your daily needs or meet basic needs. Or even if that money is ever lost, it will not affect your quality of life or you will not be paralyzed. I will not say that after investing with losing money, you will not regret it if it is somehow lost, this sentence is not realistic at all. A person's hard-earned money is always valuable and if its amount is very large, then you will definitely regret it if it is lost.
Choose money for investment that if it is lost one day, it will not have a negative impact on your quality of life. I find the definition of losing money as you have mentioned a bit confusing. According to your definition, if you need the invested money before achieving your goal, then what will you do or how will you mention it?
For me I just use the amount I can spend and don't think about that afford to lose thing when it come on Bitcoin since there's no amount I can afford to lose when talking about investing on Bitcoin. Since its like giving me losing vibes when I think about that. I have high trust on Bitcoin that it will deliver good result in future.
Somehow that use amount what I can afford to lose is giving me a vibe towards shitcoin trading since we can't deny that its really risky and we know how everything fast with these tokens that's why I think this is perfect fit when people discuss with these thing with shitcoins. Since there's huge chance to lose here, especially they struggle to recover or rug pulls is pretty common in that scene.