At 18 most kids have extremely strong passion about what they want to do. I know I did. I was wrong (maths vs computer science). But persuading them to take a break from that is going to be hard.
My experience says the opposite.
One group maybe wants to do something because it pays well, with no motivation because they aren't passionate.
The next group is very passionate about one or two things, and have lots of motivation. However, they seem to view that as the only option, even though more likely than not it will change and shift.
The third group has motivation to do work that is interesting, but they have know idea what to specialize in and have a few things they don't want to do. They aren't necessarily good at it all, and it's overwhelming to think about plans for the future because of the open-ended nature of that question to them.
This is what I've observed. And of course, people change between these groups all the time.
The second group are crusaders. They begin a quest for fulfillment of their working potential, usually despite their parent's advice, in anything they deem challenging (even in the same management or law as the first group, but for different reasons).
The last group are peasants. These will either be stepping on their parent's footsteps (or following anything they are being sold by their entourage actually), or will feel themselves lost and helpless.
...and I noticed that people change between these groups too.
As you age, you will find your interests, and passion will ebb, and flow. When I was in college, I was all about learning anything, and everything about medicine. Now, I don't even like disgusting lipid levels with family members.
In college I hated computing, and pretty much everything related to technology. I just didn't find much invented by man interesting. I felt like Programming was a waste of a life. I couldn't begin to comprehend how someone could stare into a screen for more than a few minutes. Now--I can't put this stuff down.
And to be completely honest, I still don't know how I want to spend my remaining days.