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.
Agreed, Accumulating Bitcoins even on a low income can be relatively easy if the investor understands that. Although this is a simple matter, many investors find it difficult. I would say that if one invests his little money in Bitcoin apart from his monthly or weekly expenses and keeps it going for long term then it will make a big portfolio in next 2-3 years.
Many save with fiat currency. There an investor is losing their money due to inflation after keeping their money for a long time. But if he had kept that money in Bitcoin, he would have retained the value of his real money and his returns would have increased.
One of the two things we can emphasise here is to invest regularly and hold it consistently for a long period of time. I can't give 100% assurance but depending on market analysis and future prospects I can definitely say that the investor will be benefited.