Future returns could certainly be less. But all we have to go on is what's happened so far. In the past even the worst entry+exit points are acceptable for retirement if not astounding, if you've saved something like 15% of your income for age 30-65 (I forget the exact numbers but that's more-or-less close to it). Yes, some people have to choose between cutting their standard of living and retiring on time, and retiring later for the expected standard of living. I'm not sure what we can do to change that? Like you said, we have limited time and everyone's situation is different. Go onto any of those retirement income calculators and compare the person who starts saving in their mid-30's but maxes everything out to the person who starts saving with their first job out of school and gradually increases from $100 or $200/mo.

Your comment was that equity investing can be disastrous if you hit the timeline wrong, and my only point was that unless you're speculating or are only in the market for 5-10 years, that has never happened. We have no way of knowing if that will happen in the future or not, but there's no reason to believe that we're going to see decades of middling or negative growth. There's really no other option if you want to have a real retirement unless you plan to just rely on whatever government assistance you can get.