Why do we dream what we dream?

I am a normal person who dreams regularly (thankfully, no nightmares!). Sometimes, i do remember the dreams the next day and most of the times, they are even more outlandish than a typical Bollywood movie. But, one thing which has always been the case is that some aspect of the dream would always be something which i had done or been involved with in the near past.
For example, if i were preparing for a dumb-c event, then i would not only stop at dreaming about codes, but also wake up (actually asleep) , then awaken Vidhya and ask her to decode something which i mime! Similarly, for puzzle events, i have actually got some good ideas for puzzles from the dreams.
But, a few days earlier, i had a dream which went something like this. I was traveling in a bus and got a ticket from the conductor. There was a guy next to me who suddenly dropped some coins into my hand and then asked me to hold on to them for few minutes. I, of course, wasn't interested and tried to put back the coins in his hand. But, he was avoiding this and saying "one minute, please" and so on. Then, i noticed some movement behind me and felt a hand on my pant's back pocket. I realized that someone was trying to take the wallet out of my pocket. I quickly turned around and punched the guy in his face. At this time, i came out of the dream.
No, i didn't wake up, but i went into "Analysis of the dream" mode while i was asleep. i started wondering as to why i had this dream. I had never been part of such an experience. No one had ever picked my pocket nor had i seen someone do it. i was surprised, as this ploy seemed perfect for a pickpocket gang with one member working to distract the person while another takes the wallet. Is it a sign of things to come? I dunno!