Yep it's not a guarantee!
Following this post if theres one tip I would give is for anyone who's kids are about to take their GCSE choices and A levels, sit them down go on google and see what jobs pay what, if they can select the right subjects and focus at that age it will give them a far greater chance.
The same with university, for example if an optician pays well, you can plot the path from an early age to make sure they do a degree that will almost guarantee a job rather than a generic one. There is nothing worse that studying for 16 years and realising your degree won't get you any better job than leaving school at sixteen.
If your kids aren't academic look for a trade or apprentiship, don't just let them do whatever they want with no guidence, it's probably the last time they will listen to you if your lucky, and they already don't listen to you lol