Servus!

<old cop mode>

DS has good advice. Never leave anything that may be of value in your automobile. People have been known to break into cars for items of great worth like:

Zippo Lighter
A single cassette tape
Fuzzy Dice
Bag of Doritos

I know, I did all the cases on these break-ins and the owners stated that these were the only items taken from their autos. Also, be aware that you are being watched. People who do break-ins are very likely watching to see if you move anything to the trunk or if you place anything of worth underneath the seats. I assure you, this was not some wandering bumbler but someone who does this on a regular basis. Be vigilant, don't give anyone the opportunity to make you a victim.

</old cop mode>

As for the karmic aspect - their turn will come. You may never see it, but the person that committed the act against you will have their evil turned against them tenfold. As for your question of the "I've done well, why has this happened to me?" the answer is simple. The two acts are not connected in any way. The return of your act of generosity will come at a later time.