It depends on individuals, If someone invest 30% of his salary on bitcoin, I think no matter the emergency involved the remaining 70% will be enough for any situation that may arise
What if the person is underemployed? You started your statement well that it depends on individual and by that individual I want to believe you are referring to individual needs, his income and other factors such as his confidence in Bitcoin. We must acknowledge the peculiarity of wealth distribution, which have some people living in surplus and others barely able to feed. So their investment decision will be determined by their circumstances. The percentage should not be a factor here before some persons will draw conclusion that a particular percentage is what should be invested in Bitcoin. It depends entirely on the situation of the individual.
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Personally, I think investing in bitcoin may not be as complicated as you think. Carrying out financial percentages is very necessary when investing in bitcoin. But don't forget, we may have experienced it, sometimes emergencies can come at any time and anywhere. As a result, the percentages sometimes change due to emergencies. Therefore, in my opinion, dedicating 30% of one's money to Bitcoin cannot be considered a fixed percentage. Because sometimes the remaining 70% of the salary/money earned is sometimes not enough for one month's needs. Especially for an ordinary worker or employee. So if that's the case, I think a better solution is to invest Bitcoin at the end of the month. So what I mean is, for example, in month 1 you receive a salary from the company where you work. So, don't invest that money directly into Bitcoin (30%). But first use the money (100%) for your needs for a month. Then, if at the end of the month you still have money left over after that month's needs are met and the next day you will be paid again in the second month by the company where you work, then you can invest the remaining money in Bitcoin. So by using this technique I am sure it will be better and safer. Because the point is, when you invest, all your needs are met and the next day you will receive another salary. So that invested money is good cold money to invest in Bitcoin.