I wouldn't say that there's a big "master plan" for everyone that's already planned out and can't be changed, but I do firmly believe that everything happens for a reason, to teach us something, or so that we can learn from our mistakes, or so that we can see both happiness and sadness.
For example, two years ago, about 6 months after I finished high school, my high school crush asked me out, and I was thrilled, it was exactly what I'd always wanted. Then about 4 months into the relationship, he started to lose interest, and after a year of dating, I broke up with him because he was cheating on me with a close friend of mine. It was rough, but I learned that people aren't always who you think they are - everyone thought he was a great guy, we were all shocked that he'd do something like cheat on a girlfriend.
And if he hadn't cheated on me and I hadn't dumped him for it, then I wouldn't have started going out with my current boyfriend, who's a total sweetheart who treats me like a queen. If I hadn't had that bad relationship, then I wouldn't be in the relationship that I'm in right now, and I certainly wouldn't appreciate it as much as I do.
That's just one example from my personal experience. I've had lots of things happen to me, and I try to learn from everything. I believe that nothing in life is pointless, there's reason for everything, otherwise, why would it happen??
But that's just my opinion.