Figured out the hard way that it's not the best idea to keep everyone happy. Providing higher education to everyone seems nice, but the city gets to a point where 75% of people are overqualified. The only orange (industrial zones) that employ highly educated people are offices, level 3 normal industrial, and oil (finite resource and after about 2-3 years you exhaust a "patch"). High density commercial also employs them. So if you have any forrestry, ore or farming (or level 1-2 normal industrial) you're employing too many overqualified people. If you can't provide enough good jobs people are going to start leaving. But even the top buildings employ educated and well educated people, so if people leave they're going to redistribute their workforce and once again you'll have overqualified people. Eventually your city is going to implode on itself.
You can't skip industries either, because then you're just going to end up importing everything and that'll kill your taxes and therefor your economy (if your city is big enough it has huge expenses)... and traffic. Only really started being a problem at 100K+ people though.
I suppose the game is meant to be played more "realistically". i.e. there are better districts and there are worse districts. Can't really build a utopia