For example, if someone invests and spends a lot of money on it. If he spends more than his stable income, then he may end up in debt and have to sell his holdings.
I think you are a bit confused in what you are actually saying here, what you should be saying here is that you shouldn't invest more than your discretionary income because anything done outside that smells trouble for your holdings, as long as you are doing it from your discretionary income, you have no worries.
But take note that your emergency funds and backup funds needs to be set aside from there in case of any real life emergency that may arise in the future.
Create an emergency fund equal to 3 times your stable income.
With this statement here, it shows that you are even more confused with your choice of words, I believe that what you wanted to saying is your emergency funds should be big enough to Carter for your basic needs for like three months if their is an issue like lose of job in the future.
They would really get a problem if they are using the whole earnings they get from investing on Bitcoin since they might lose from any bad situation especially if they don't know how to handle well those bad situations occur.
That's why its advisable to use your discretionary income since for sure that you will not worry about anything since that fund is somehow the money you can afford to put in your investments.
Also I'm confuse about what he said that your emergency funds should be equal to 3 times of your income since what has been recommended is it should last for 3 to six months of your living expenses.