My guess is anyone who has an investment in bitcoin without having an emergency fund in fiat, then sooner or later they will sell their bitcoin. At least 20% - 40% of the total investment budget must be saved as an emergency fund, this will definitely help them if an emergency occurs.
I am not sure if there is a need to set aside any kind of specific amount (on a regular basis) in order to maintain your emergency fund, yet there are a variety of ways to assess whether your emergency fund is enough, including some kinds of considerations that if your cashflow were to dry up for six months could you still survive? or if your expenses (also) were to go up for 6 months, or maybe both negative events happen at the same time, and in that regard, from where are you going to draw in order to be able to survive during that period in order to hopefully also attempt to be able to secure additional cashflow or to reduce your expenses back to levels in which your income is greater than your expenses... .so yeah, it may well not be prudent to be investing much if any into bitcoin while you are building your emergency fund, even though surely sometimes we can still start to invest and know that we are building up towards reaching a certain target (in terms of either building our emergency fund or maybe even replenishing our emergency fund if we had to draw from it at an earlier date)...
Some schools of thought would suggest not to invest at all into bitcoin or into anything else until you get your finances in order - even though I understand that sometimes there are not necessarily going to be strict rules, but ways that any of us might exercise caution and/or moderate investment approaches while we are getting our various finances into a better status (in the event that we might have some issues (problems) in regards to either the level of our cashflow or the level of our expenses or both).
Ultimately we are in charge of exercising our own judgements, including needing to take responsibility if we screw things up, and whether or not others are hurt from our mismanagement of our finances is part of the process of taking responsibility, hopefully learning along the way and hopefully improving our practices along the way.
You are right, maybe that has happened a lot when they already have assets in bitcoin while fiat money has never been reserved for other emergency needs, the safe way is the method above by balancing what our needs are.
20% bitcoin investment
30% emergency fund
50% as our daily needs/months
I think that's more than enough.
I doubt that there are any strict formulas regarding how much to be in your budget for any specific category, and sure we can create formulas and targets for ourselves that might help us to attempt to create and/or to reach certain goals that we have created, and surely some folks have more discretionary income (which means money that is free to do whatever that you want with it because it is in excess of the money that you would need for expenses and/or in excess of any money that you might need to build or create an emergency fund) than others, and if you have a lot of discretionary income, then you are free to use more money to buy bitcoin with it.
And, yeah, to some extent, you might be able to create your own discretionary income or your own discretionary levels by figuring out how well your finances are in order at the time that you get into bitcoin or otherwise make your assessments about target levels of investment that you might want to achieve and how much that you are able to dedicate to such bitcoin investment process based on how much income that you have coming in versus how many expenses that you have, and sure you might have some months in which your income and your expenses are consistently the same, but you might have other months in which you might have either great cash surpluses or great shortages of cash for a variety of reasons that might have to do with irregular expenses or maybe even some "surprise" expenses... when you have surprise expenses within a particular month, for example, you might be faced with some dilemmas regarding whether you should still invest into bitcoin during that month or to cut back with your bitcoin investment or to completely withhold your investment into bitcoin until you are able to get your cashflow/expenses ratio back in order and perhaps aiming to replenish your cash reserves prior to resuming investing into bitcoin, too.