The market return for the past century has been something like 7% (after inflation). If you're investing in time spans longer than 10 years then typically you expect something in that range.
Past performance does not promise future results, and the world could end tomorrow, but it's not a bad idea to plan that you'll get an average of 5%+ on market investment.
(I'll note that you're responding to someone saying "pretty much guaranteed" and dropped that qualifier in your question).
I know about that, I meant besides that. An average return doesn't mean a consistent return from year to year - e.g. $100,000 / year from 2 million. I was just curious how other people would invest to target a high probability of 5% each year.
Past performance does not promise future results, and the world could end tomorrow, but it's not a bad idea to plan that you'll get an average of 5%+ on market investment.
(I'll note that you're responding to someone saying "pretty much guaranteed" and dropped that qualifier in your question).