If someone is putting money into Bitcoin without having any discretionary income, it is almost like they are setting themselves up to fail because the moment life throws them an emergency, the first thing they will do is panic and sell off their Bitcoin at the wrong time.. That is why emergency funds and discretionary income almost go hand in hand, like you said. If you have a cushion aside, you don't feel the pressure to liquidate your stack. I would even add that it’s not just about emergencies, sometimes opportunities come up in life, and if you have no spare funds (separate allocation), you’ll be forced to touch your Bitcoin…. Having those safety net gives you peace of mind to truly hold long term..
It has been proven that we can only succeed in holding our Bitcoin investment for a very long time if we use discretionary income to invest in Bitcoin. So if there are investors that are not using discretionary income to invest in Bitcoin, they won't succeed with Bitcoin investment because it's obvious they are using the money meant for their expenses to invest in Bitcoin, and they will surely sell their Bitcoin too early to solve their expenses. That's why it's advisable for every investor to prioritise using discretionary income to invest in Bitcoin so that we can always take care of expenses and free ourselves from being under pressure to Bitcoin for a very long time.
This is true those who invest in bitcoin without using their discretionary income is only gambling with their investment because bitcoin investment is not like other investment that you will invest now and expect profit soon, it is a long term investment so using your discretionary income is the right approach so you won't feel bad if things didn't turn out as you expected.
Yes, an investor must first understand that Bitcoin will never bring him quick profits, it will only bring success in the long term, so he must invest money that he can hold for a long time without any such problem, and for this he should only decide to invest from prudent income. We can never say exactly where Bitcoin will go in the future, everything depends on uncertainty, so you should never decide to invest with money that you cannot afford to lose, so after meeting all your necessary expenses from your income, start investing only with the amount of money left (no matter how much smoll the amount), this will continue to grow over time.
Fact, I will also add that the mindset behind the investment matters a lot.. Many people go in with the idea of let me just hold until it pumps, but the reality is Bitcoin does not move on our personal timeline. Sometimes it takes years before those small contributions really show their worth. So apart from only using spare income, an investor also needs to train his patience and detach emotionally from the price movements.
If you invest and keep staring at the chart every hour, it will drain you and might even push you to sell too early. The people who win big with Bitcoin are usually the ones who manage both their money and their emotions..