Next Step After STPM is?

I have asked before a lot of people from my sixth form class about what course they want to study next after STPM. At that time, we have not sit for the exam yet. Anyway I thought those who have came in to Physics class in Form Six should have already know what they want to study, but a lot of them have not decided yet.

Anyway, I have started thinking about it right after I finished my STPM. I kinda thought that since I like Physics I thought that I should go for a career in Engineering. But liking Physics and scoring good Physics grades aren't going to promise one a brilliant future in engineering (an analogy to that of medicine: interest in biology and fantastic grades in Biology aren't gonna guarantee that person is going to graduate as a medical student and become a doctor...)

The thing is that we kinda need to 'predict' that we would succeed in the field that we choose right now. One might be so interested in course A, and so thought a lot before joining. But maybe two or three years down the road he or she might lose interest and drop out. Not that that person does not persevere. One can't force him or herself to continue studying that course if that person don't have interest in it anymore. Also, not that he or she did not do optimum research in the course or the profession that the person want to take up. I mean: how can one know that what he is seriously interested in right now, will equally interest him few years down the road?

Really REALLY CONFUSED right now what to study next...