That is the point of the problem, sometimes we are not unwilling to allocate our income every monht in a large percentage amount, but with the economic situation that still has to divide on other things that ultimately make us as minimal as possible to allocate it. That is not something wrong either, because there should be no compulsion that makes us ignore other needs, because if we do that it is something that is not wise either.
The most important thing when we do this is consistency, for me it doesn't matter when the percentage is more flexible, especially when our financial situation is up and down.
30% is a fairly large allocation because for me it is a very aggressive step in investing. However, as JJG said, those who do not have large expenses for their living are certainly a better choice to save themselves in their investment plans. Well, if they are able to survive by allocating 30% for up to 3 years, of course the achievements in BTC ownership will be quite large.
Apart from that, all the dependencies and unexpected expenses in life can also affect the level of allocation in investing each month. However, every plan has to be thought out properly beforehand to prevent chaos in their investment journey. Well, in my opinion, most of them are probably only able to allocate 10% to 15% of their income to invest.
The percentage depends entirely on the income level of the individual as there cannot be a general rule for determine the percentage of income to set aside for investment. For those gainfully employed using my country as a case study, living expenses is not more than 20% of the total income so someone can even allocate up to 50% of their income to Bitcoin and will not be affected in any way. unfortunately, not everyone have this kind of job or business. On the other hand, there are people that their total income do not even meet their basic needs, this makes it practically difficult making investment when basic needs have not been met. Finally, the average people can allocate as much as 10% of their income and still do well with other needs.
Different people with different appetite as far as investment is concern and what governs the general approach is the target. If you target to accumulate a certain quantity of Bitcoin in like five years, it becomes easy to calculate your income and how much you can set aside to buy through the DCA method or any other method that seems convenient for you. So, the target, conviction and faith in Bitcoin are some of the things that determine the percentage of income to be allocated to Bitcoin provided basic needs as well as provision for emergencies have been made.