Although you are right, we have to remember that the formula is the same in trading and investing. That is, invest and trade with the amount of money you can afford to lose. Only when you are able to lose the amount of money will your energy and inclination towards investment work, but you will not be emotional. Many times it is seen that people are afraid of investing, but instead of being afraid of investing, they participate in the investment with the money that they can afford to lose.
What you really mean is that both investing and trading involve risk. Those who are going to invest or trade should invest with risk because sometimes you can make money from investment and other time you can lose your money from investment. So invest as much as you can afford to lose.
Firstly investing and trading are two different things meanwhile if comparing the risk involved I will consider trading as a risky move but, this topic is not about trade and if anyone should trade they should be knowledgeable first but still doesn’t give full assurance. Investing is more safe because an investor will hold for long term with what’s available, this statement is kinda complicated “ invest as much as you can afford to lose”, bitcoin investment is not like gambling when people are given such advice to gamble with what they can afford to lose. The lose you mentioned simply means some day everyone might just not see any profit as anything attach with lose makes no progress. Bitcoin investment has no lose except the investor doesn’t want to hold for long that’s when we can say an investor is taking a risky move but, if we’re holding for long term we should expect profit in return. All what an investor needs is just the right strategy that suits their investment and a long term plan.
In this comment you did mention 3 different things, which are TRADING, INVESTING and GAMBLING, but I rest assured that if one knows the difference between these 3 things, the person will be able to know the one that's risky and the ones that's not.
However, investing and trading are 2 different things and one should know that investing is more mature than that of trading, but what makes it a little bit similar is that you risk money on them. One of these 3 is considered for less risk.
And applying emotions on things like trading or gambling is not good because your emotions will make you lose and there's no doubt that you will lose more money once you are chasing losses. But on investments, even when you are losing, you don't have to panic because as time goes on you will recover your losses (but that's when you are using a good strategy like DCA). If one is using emotions to invest, his investment won't end well, because at every loss, he/she won't be happy. Before I forget, we must learn to invest with the amount we can afford to lose in others to avoid including emotions in our investments.
If it happens that bitcoin crashes which I know is impossible, due to some unknown circumstances or in future a better channel of wealth was introduced that made people start abandoning bitcoin for the new technology, you will not lose all your life savings. I think those are the two reasons which I know why that word invest with the amount that you can afford to lose is used. There is an extend that you will invest those little amount of money after 4-10 years you will be surprised at the amount it has piled up to.
Well, there's no doubt that it's impossible for Bitcoin to be replaced.
Investing a decent amount is also another way to say invest with an amount you can afford to lose. Even if one is responsible or irresponsible, he/she should know that it's very important to invest with an amount that they can always afford to risk. Everyone has an amount that they can afford to lose, but most people don't know.