The problem with that is that your COL in those 10-15 years is significantly impacted. That's probably 10% of your entire life. While I understand some people might be comfortable with the tradeoff... its important to remember there is something you are giving up.

I don't think I understand what you're giving up in that 10% of your life.

I'm living in a studio, have a parking spot, walk to work and go out with my coworkers/friends after work.

What am I missing out on?

After tax? Sure, it's possible, but there aren't actually that many people who make $300k/yr.

$100k after tax is only $140k pretax

Eh... sure, if you're only paying federal taxes. But in on that $140k you're going to end up with about $92k. And everything is more expensive in cities. The idea you're going to live in SF and save more than about half that, even living like a monk, is kind of fanciful.

NYC is even worse - lop another thousand off and pay even more to live.

I've personally lived in both cities and you can live perfectly well on $4k a month with a couple of roommates. Better than the average American even.

Then, if you invest $46k a year for 15 years at a real return of 4% you end up with ~$943k in present day dollars which is right around what the parent was saying.

Not to mention $140k total compensation is relatively low for a senior dev in SF/NYC, you will likely be making a lot more 10 years in.

Where are you going to get a real return of 4%?

US stock market has averaged 8 over the past 50 years

That's unlikely to be true in the future for a whole host of reasons.

You will be making $200k+ in SF even in your early years, if you climb the corporate ladder you can get to $300k in 5 years.

You can definitely sock away enough even without a 4% rate of growth to put away $1MM of after-tax money in 10-15 years, if you're smart with your money.