Yeah, it's not an impossible pipe dream for a lot of people. I agree
But the calculator that I've got open is telling me that it'd take 35 dedicated years of socking away $2500/mo at a 6% return rate in order to hit $3.5M. Not impossible, but I think the "without a lot of pain" part is subjective.
In your 20s, you tend to have more disposable income, but significantly lower take home pay, so $2500/mo can be a lot of cash when you're trying to get on your feet with buying a home, getting married, etc.
In your 30s, ok.. you've doubled or maybe even tripled your salary, but kids eat that "extra" cash up in a hurry. Travel ball and what not...
In your 40s, now you're making pretty good money, but you're saving for college, weddings, kids' insurance, etc.
Then from there, like I said... you just have to hope and pray that a divorce, layoff, major health issue, or something similar hasn't bled you dry, and this all for a couple that I'd consider to be pretty financially responsible. i.e. No $100k cars, extravagant trips, etc
I agree with you. It can be done, but not often without some very strong dedication and good fortune