If one lives a modest life (no Ferraris/Great-Gatsby-parties), on a sensible financial management, one can have north of £/€/$1m on the side, in one decade(speaking for UK/EU/USA)(for contracts on IT/IT Sec/GRC/PM.
That type of savings goes beyond "no Ferraris/Great-Gatsby-parties".
For example, let's say I increased my bi-weekly savings by $150. Because it was pre-tax, with the tax savings I was still saving $150 but my take home only went down $100.
By the time I want that money, I shouldn't have a mortgage payment so I'll need far less money than I'm making now and my income tax should be much lower, not to mention the additional gains on a higher principle.
So without giving financial advice, I'd say it's more complicated than throwing it in an index fund if your time-frame is a decade.
We aren't talking about losing sleep over volatility here. We are talking about a situation where someone specifically wants to hit $1M in a decade.
For example, I put several thousand in a Vanguard TR Fund in January of last year. It's still down 2% overall. Now on a 30 year horizon, no big deal. But for a decade that will significantly impact the compounding returns. Stocks are very volatile and may not be real desirable for a 10 year time frame.
Even a ten year average returns is typically going to require more -- a cycle longer than twenty years. Financial services are sold: caveat emptor.
Let's say a 7% annual compound interest over 10 years (which I think, is debatable). That puts you at $5,800/mo. I think my argument still stands?
Once you hit your number, work gets pretty depressing. You realize you're making more from passive investing, just doing nothing.
I can do 2.5k a month as a not massively well paid employee