But from what I've noticed, most people don't keep track of how much money they have, how much they're spending and how much they need...
I would say that this depends on your financial capacity. Plenty of people live paycheck to paycheck, and they almost certainly keep track of what they spend and how much they need. You can obviously afford to ignore more as you amass more of it, but even at comfortable levels, I'm sure people are keeping track of how much their next holiday is going to cost, how much they need to make for that dream car, etc. Even Bill Gates must be paying attention to how much certain things cost (maybe that next jet or private island lmao); it just so happens that normal grocery items are already so far beneath him that he couldn't even come up with a range.
It can be easy to fall under this perception if you're satisfied with where you are, but ultimately, it's not just a number. The only time you don't realize that it's there is when you don't need to use it for anything.
I think if you get really rich that you don't care about money anymore is the right time for you to say that money is just a number. But if you're not that rich enough and still the money matters to you then the value of money is just a number for you. You will regret losing your money when it happens that will serve us a proof that the value of money really affect your mental health. How much money it is needed for the value of money to become just a number. When you try to spend money without even looking on the price because he price of a certain things doesn't matter to you anymore. That's how rich people think when they are too confident in spending their money and thinking it only just a number.