The point is that you only need to do that for a few years.

Let's say there are 2 people.

Both earn 300k takehome.

A spends all of it.
B spends only 36k and invest 264k a year (let's just say 22k monthly in bonds of 4% interest per year).

After 5 years at the job, A has no savings. B has $1.43M.

Now, recession hits. Both lose job.

A has no choice. He has to go find a job even if it pays less than 300k because he has expenses to pay.

B can literally just live off the interest of 4% per year which is 57k a year or 4.7K a month if he wants to while taking his own sweet time to find a job that pays him 300k or more. He will in fact even has excess because his expenses is same as when he earning 3k a month.

Now, I used bonds as example. Imagine stock market.

Compounding interest is the key. Literally earning interest on interest.