Its the lower starting salary and delayed entry to the workforce.
Well yeah, luck always plays a role when it comes to getting advantages in life. In the lifespan of 43 years though, I think this number is long enough to use strategy to minimize the disadvantage from bad luck. I know it's hyperbole, but I wouldn't use "life is ***" to describe someone graduate during a bad time.
Certain life choices sometimes get people drastic advantage but for whatever reason it isn't encouraged, which is always mind blowing to me.
For example, living with parents, even when you have a job and married. This saves your rent/mortgage and it can help you save $500 more per month. After 43 years that extra $500 you put in SP 500 every month can add another one million dollars in your portfolio due to compound interest.
In my culture, living with parents even after marriage is a popular choice, about 30%+ of married couples choose to do that. But it seems that in English speaking world living with parents is discouraged or even laughed at. Which, IMO, just leads to more lower income people having money problems because their monthly saving is $500 less per month due to rent/mortgage.
This kind of life choice is simple to make, but it makes all the difference in the world after 40 years.
Same can be said for owning a car v.s no car. Buy your Nvidia 5090 or don't buy, go on a trip or don't etc. every small money decision like this, can add up in the lifespan of 40+ years as compound interest from savings snowballs. And IMO, the difference between lower starting salary due to bad luck eventually become irrelevant.