If your friend has found success in an asset, that's great! But it doesn't guarantee that you will also find success in it. The very basic of investing is - always diversify. So I would not recommend to depend solely on Bitcoin.

If you have income sources from business or job, continue investing in multiple types of assets like precious metals, stocks, bonds, real estate alongside Bitcoin. It is very important to keep a balance.

Depending on single asset may bring unnecessary hassles and increase the risk factor. I personally wouldn't recommend that!

Storing all your assets in Bitcoin is a bold and daring move, but I don’t think it’s wise, because you’ll encounter fluctuations. You’re right about what you said about your friend, sir. Relying on Bitcoin for 99% of his assets means he doesn’t have a stable economic mindset or is a Bitcoin maximalist. I don’t judge whether he is right or wrong in what he does, as it ultimately depends on his own circumstances. The question is, does he have the mental fortitude to endure for the long haul? Because we are currently in the final phase of the Bitcoin cycle.

Is he a trader or an investor today? Because those are two different things.

Unless he is still selling his art and has active income from his business, then he saves the remaining profits from his business in Bitcoin after his needs have been projected to be met.

A wise man once said, "Do not carry all your eggs in one basket." This could be applicable to all spheres of life including business. As a smart businessman, diversification should be a must because not all sources of income can be that stable not to talk of when it has to do with cryptocurrency. We all know how the crypto market could be volatile which means it can not guarantee you a stable price as it fluctuates frequently.  

Your friend should not just pack up his wonderful career just because he found crypto to be a reliable source and has gotten a fortune from it, he should see it as an alternative source of investment while he continues with his work so as not to let it just die like that. He doesn't know what the future holds and a such should be enough reason for him to hold onto his business while he takes crypto investment as an alternative. He packing up isn't a wise idea but rather I would say he is just testing the rivers which I think is not safe for him to take such a step.

If the business is successful, why stop doing it? Why deprive yourself of a reliable source of income?

Either your friend is not quite sane, or your story is not quite truly true.

Regarding "making all bets on bitcoin", you are right, it is quite risky and for this purpose diversification was "invented". No matter how promising bitcoin (or any other asset) is, it is wiser to invest only part of your income in it, and divide the rest into other types of assets (real estate, gold, business or even a bank deposit or a wad of money under the mattress).

I don't know when the OP is going to come back to answer a few questions, as there is no clarity as to what your friend does with Bitcoin, whether it's investing in Bitcoin or day trading it, which is where he makes his money from, because if it's investing and holding for a short period of time, your friend can't even think about leaving every other job he does for that, based on the type of profit that he will see, and he might not consider it to be enough.

Bitcoin or not, it's not advisable to throw all your resources into a single investment. For in the same way we advise people to find themselves into more than one means of making income that is how it has to be with investment assets. You have to spread it to other areas while you still have a source of income to cover for daily needs. Op, your friend have to realise that there are bearish season with bitcoin and how does he survive in those periods since he has quit his artwork which was a source of income he once used to invest into bitcoin from the beginning.

Depending solely on Bitcoin is like living in a world where the only color is orange. It is brilliant, but you will miss the blue, the red, the silent greys. e protocol has poetry in it, the scarcity has elegance, the freedom it gives has fire. Bitcoin is resistance.  It is the rejection of the world where your work is bled out by inflation and manipulation. I would trust it more than any fiat hallucination on offer.

But, take a deep breath, risk is not evil, it is oxygen. Bitcoin was born as an act of rebellion, not as a safety blanket. Every block mined, every transaction, every node, these are acts of defiance, but also acts of exposure.  When you are all-in you are all-exposed. A crash can come at midnight; a pump, at sunrise. No central bank is coming to smooth the ride.

When your friend invests all his soul, sweat, memory and survival in this single revolution, he is no longer immune, he is vulnerable. Bitcoin is the king as it is the only one, but the humans who use it must have more than one pillar to stand on. These are the basics of art, craft, skills, which make sovereignty worth anything.

Digital freedom should never enslave you to one result. Stack stats, make art, run a node, plant a garden, tell a story. Do not trust, verify, then diversify. The revolution is here, but even revolutions need backup plans.

Ask yourself: How many ways can you win? That is where the real freedom lives.

There is so much risk investing in bitcoin, so I wouldn’t suggest to invest all in. Your friend is doing the scariest move, trusting all his resources into bitcoin, which we do not have guarantees what will be the future price of bitcoin or how long will it stay in the market.

However, I would admit that bitcoin is the most profitable crypto investment so far, but due to its volatile nature, the risk to lose is always high especially if you don’t know how to practice proper risk management. It’s better to still look for a main source of income and just make bitcoin investment a side hustle.

Bitcoin is a very good investment and one of the best in the world right now, Bitcoin is a very good asset however I really don't support someone having Bitcoin as his or her only investment but if you are still growing your Bitcoin investment I don't think is a good idea to diversify to another investment immediately because you will lose concentration at some point and if you are not careful you will end up losing your Bitcoin investment and the other investment you decide to diversify into, so is better you focus and build your Bitcoin investment to a certain level and then you diversify to another investment.
I'm not saying one should diversify because I don't trust in Bitcoin is because having only one investment is not a good one, no one can tell what may happen in the future so having different investment will help you keep your wealth going, there are some people that where very rich before but right now they are poor and the reason why they are now poor is because there only investment failed, so is only better to have different investment it gives you more money and also give you confidence in life.