It used to be one of the most common questions after I say I was a photographer, when I was younger. Somehow I stablished now. I live from it. Freelancing is by definition unpredictable and you have to stay open for the changes and risks attached to it. There have been times where I have a lot of money and times when I don't have as much and after 11th years I have learnt to juggle and be mindful with investments.
In the Dutch law, being a ZZP'er (freelancer without other people working for your company directly) involves having more than one client. And this is important for you to balance, the long term clients that maybe pay less per shoot but add to your business a different sense of security and the short term clients where you can charge more per shoot but it is a once in a lifetime project.
On the first years I invested most of my profit in gear. I am not addicted to gear like many hobbist, I mostly just want to know and own what I need to the next step to grow. I don't want a new camera all the time (It is pretty annoying to have to learn a new camera all over. I just want my trusted old camera as long as it can deliver high quality).
Living from it also depends on the lifestyle you want for yourself. I would not know what to do with a yate, for example. I want to shoot in it once and then go away. So, I have the life I want by having enough for all the things I need, what I need to invest and have more of the things I value. I am ambitious, but I am aware of what I need and I what I don't.