It amazes me how many people don't do this. One of the most humbling exercises one can do when going through this process is to start by calculating all of what I would call the 'base costs'.
Essentially: housing costs (mortgage, rent, maintenance, Council rates), food and groceries, utilities, insurances, kids schooling, sporting and extra curricular costs (for those with kids), transport, recurrent medical expenses/medications (if applicable), basic sport/fitness costs for staying fit and healthy. Basically, what are the base costs to just keep the household running. Then average these costs per fortnight/per month. My wife and I did it years ago before having our two kids and have maintained and adjusted over the years. It's a way of saying "What is the minimum we need to be making in order to live and keep the household running?"
Put into context, I am quite prudent to even frugal with money (so is my wife), so we don't spend on expensive things. Grew up partly raised by depression era grandparents, who's values and attitudes around money were very much instilled in me. We are in a situation where we fully own our modest 1950s bungalow (so no mortgage or rent), we have no car finance/leases (I buy cars that have already done a fair amount of their depreciation and keep them until they basically die). Our kids are at a government school (so no private school fees) and do a couple of club sports. My wife and I play a bit of cheap club sport and I just go to a local community non profit gym for weights (no expensive gyms and/or health clubs for us). Yet it still costs us the majority of my wife's salary to cover these base costs. And she is on probably a median public servant's kind of wage. Hypothetically, if we ended up on just her income because I got structured out of work, it would take most of her fortnightly wage just to keep things running (again stressing, we have zero debt, don't pay rent or a mortgage and don't pay private or even Catholic School fees either). That is how expensive just living is. And I don't think people have any concept of how much of their income is going on these "base costs." So really have no concept of how much is truly left over.
And therefore extending on what you are saying, it goes some way to explaining why many just stay on a hamster wheel, not really knowing or pinpointing why they aren't really getting ahead. And any change in circumstance (time out of work, interest rises, unexpected bills etc) is enough to send them into oblivion.