To be honest, I've had a great deal of trouble reaching the top of careers in what I would think is a decent amount of time. I feel like it's far too difficult to get a promotion in my games. I always have the right mood in the morning with all the tasks (daily and otherwise) completed and it still takes days of even "work hard" to get a promotion. I'm starting to get frustrated because I feel like I'm doing everything right, though my Sims never seem to have a life outside of their career when they have a career, and if they do have a life outside of their career then they're practically being demoted/stagnate in one place.
The only career I've made it to level 10 thus far in is the painting career, which has thus far been the easiest career for me to max. I'm doing a legacy run through to try out all the aspirations, and those are fun, yet I can't seem to figure out careers properly.
Perhaps it's a learning curve or something that I have yet to grasp with this game, but I feel like I'm either not doing something right or perhaps doing a career path is too hard. Looking at that "Play as many careers as possible" challenge just intimidates me though, as I doubt I could even get through one, let alone more.