While it's true the market has given guaranteed returns well north of 2.2% average for 30 years or more (the single worst 30 year period would of been higher than 2.2% average). However, when you cut that down to a decade it changes the picture significantly. There are decades where you could of actually seen a loss.
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.
Don't overthink this stuff. Most of the decades you wouldn't see a loss, so you're better off investing a good chunk. Keep 10 to 20% of your holdings in cash getting 2% interest if it helps you sleep at night.
I wasn't trying to overthink. But the market is volatile at the moment and the next decade is rather uncertain. Thinking you can just throw your money in and get 7% over the next decade and get to $1M may not be the best strategy.
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.
I'm not suggesting one time the market. We've been in a huge bull run in the last decade volatile or not. But if you are shooting for $1M in a decade you might want to think about asset allocation more carefully than 100% in the market. That's all I am suggesting. I agree for the portion you are allocating to stocks, DCA in and don't try to time the market.
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.
I'm all for buy-and-hold, but you do realize that there's a group of people for which this is very hard? Psychologically, they'll have trouble staying the course when seas are rough.
With ongoing contribution plans like retirement accounts, the thirty year average returns are relevant to a sixty year contribution cycle: Assuming no back loading (later contributions larger than early contributions). With a back loaded cycle, dollar by dollar thirty year averages require a greater than sixty year investment cycle.
Even a ten year average returns is typically going to require more -- a cycle longer than twenty years. Financial services are sold: caveat emptor.
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.