and we have to fight as hard as we can.
and invest in btc in my opinion need an investment trading strategy and so on.
and usually many people are forced to sell btc because of emergencies such as illness,
Well, to invest in Bitcoin, you don't have to fight for it; you don't have to struggle for it. What happens to some people is that they lack the right investment ideas and management. Someone is not supposed to invest in Bitcoin in a way that could interfere with their mental health, like investing when you cannot have a peaceful sleep because you are either bothered about the Bitcoin price fluctuation or because your supposed period of investment is about to elapse (like if you just want to invest and hold for some months with the hope of making profit within that period).
Bitcoin investment is supposed to be done in such a way that you don't have to get so worked up about anything or even some arising emergencies. Let's take, for example, someone who is working and earning $500 per month. He or she can make a budget for their needs in a month and decide to invest just $100 into Bitcoin every month and use the rest to settle their needs, but some people would just invest like $400 into Bitcoin and assume they can use the $100 to cater for their needs in that month, and if they are unable to manage that $100 for that month, they may be forced to sell some Bitcoin, and they might be selling it when the price is lower than what they have bought.
Although it might not be all, but some people are forced to sell their holdings because of a lack of planning on how their investment should go. They don't budget very well to know how much they are supposed to spend, how much they should keep in fiat for emergencies, and how much they should invest that will not affect them in any way. When all that is handled, the person will not be forced to sell their coins in just some situations.
Practice can bring a lot of improvements, and sometimes it could take a few years to really start to get used to how aggressive a person might be able to be without becoming overly aggressive in terms of how much to invest in bitcoin, how much to use for expenses and how much to keep in some other kinds of emergency funds that might not be linked to the price of bitcoin, but instead linked to the fiat currency in which expense might be accounted, and for sure, over 2-4 years many emergencies can happen, and it is not good that the person might have put themselves into their own emergency because they were trying to be more aggressive than they should have had been, just like your example of a person with a $500 monthly budget spending $400 on bitcoin when maybe that person should start out with smaller amounts, such as $100 and maybe build up to $400 later, if $400 is even reasonable at all.
There are likely ways to also consider an investment budget in terms of a percent of the cashflow.. maybe start out with 10% and then work towards higher levels, but at the same time, many of us should be able to count up all of our expenses, but sometimes we also have difficulties being able to identify the variances in our cashflow and our expenses, and if we are able to plot out our budget on Excel spreadsheets or some kind of a easy way to keep track then we can try to both attempt to identify past issues but also attempt to project out future cashflows in such a way that we always have a bit of a budget cushion, too.. so it becomes less likely that we will have various cash crunches, and we might even be able to better see potential cash crunches that might come at future dates that might be based on various payment plans that we might get into and also even various ways that we might generate cash in the future that may or may not contribute towards greater abilities to have a cash cushion and also to potentially be able to invest in bitcoin now or in the future based on our cashflow projections - and hopefully we do not overly anticipate and we error on the side of NOT having as much cashflow and having more expenses.. and ONLY committing to buying bitcoin with our extra cashflow when we know that our cushion is fairly and reasonably projected into the future.
By the way, recently, I had gone out and projected out my cashflow until the end of 2024.. and I made some changes in some of my projected expenses (and to increase and double some of the categories) assumptions.. and so then when I went out and made the increased expenses changes, I saw that there were a few different months down the road that I would have some cashflow shortages based on my updated/amended projections - and I am glad that I when through the process of making those changes, so I can anticipate those shortage periods in advance and be in a better place to prepare for them, including having ideas from where I will draw the extra money in the event that my projections end up playing out and I don't have enough cash on hand to cover the expenses during the various shortage periods that I currently have projected out towards the end of 2024 (and that is ONLY projecting out about 20 months.. with the nearest 3-4 months being more important - and more of a potential crises - if there were to be some cashflow shortage considerations - as compared to the further out months).