Firstly, you tend to live within your salary terms: you get a nice home, you spend a little more on the luxuries of life and you find each month that you don't have quite as much left over as you would expect.
You don't need to be showy for this to happen. I know people on equivalent salaries who don't own cars and live in small flats who don't have a lot of spare cash.
And then you have the freedom aspect of things that ties in with this: because you are never really sitting on a big pile of cash, and because the bills are coming in regularly you feel trapped. You need to keep on making a decent amount of money, and therefore you end up working for somebody else on something you're not too happy with in order to just stay where you are. Meanwhile, the industry moves on and you feel as though you're stuck in the same place and eventually you'll get eclipsed, so you throw yourself into staying ahead and all you're doing is running on a conveyor belt.
There's no easy fix. What I suggest for your friend is to focus on that concept of freedom.
There is a metaphorical story for your friend about a tramp and a greedy millionaire. The tramp proclaimed that he was the richer man because he had all the money he wanted, yet the millionaire was compelled to keep working because he wanted more. Who was the freer?
Live on less. Stockpile the cash. Realise you can buy a home outright with a few year's savings and be free of rent or mortgage. Move and keep stockpiling the cash. Grow food. Do more with less. Realise over time that you're spending virtually nothing and you can live on that stockpile for 5 years. Then 10 years. Then 20 years. Then realise you're free. Stop working for somebody else. Throw yourself into something you love.
I've been in a similar position to your friend - the only way out realistically is to live on less. Chasing more is a fool's errand as a first step. Make do with nothing, spend your time on something you love, and then the opportunity will arise to have the freedom to do something more.
This idea that you can become a millionaire by writing some apps or mining some Bitcoin is one of the most toxic and acidic things in our (development) culture right now.