Bitcoin investment is not a daily business so it is not advisable to live solely on Bitcoin investment and even trading too is it is not advisable. But you can take it as a side hustle. But when it is low and sell when it is high. That is the method most investors are doing.
And it is good you are doing business before your invest in Bitcoin because you will be tempted to used up the investment coins. But if you are doing a business it will be a plus to the investment because your daily bills will be channel to the business and not to the investment.
I understand your point, and it seems you're correct.
If you rely solely on Bitcoin for trading or investment, you still need to meet your daily needs.
Making money with Bitcoin can be quite difficult, or perhaps very risky. Bitcoin investment should be viewed as a long-term strategy, or can be utilized in your business as a payment method.
Generally, people are now using Bitcoin as an asset.
@OP, just let your friend know he is making the wrong decision.
It could jeopardize his life or financial situation.