A sequence of return risk means that if you are a retiree and you are taking money out of your portfolio, you face some different challenges from say a buy and hold investor. So imagine you're a buy and hold investor. It doesn't really matter how the market performed along the way.

The only thing that matters is your average return over those 30 years. So that determines uniquely what the final outcome would be. Imagine you had something like a 10% average return between now and the end point. And it doesn't matter if you had poor returns first and then very good returns later on or vice versa.

That's true for buy and hold investors, but it's not so much true for people who are putting money into their portfolios. It's actually the flip side of this. It turns out that for retirees, it's not so much important what the average return is over your 30 year retirement horizon.