first off, i know i cannot PROVE karma exists to you... i guess i will just share some thoughts on the idea of it...

i always look at it as the unseen version of one of newton's laws of motion... for every action there is an equal and opposite reaction...

does it work that for every good thing done there will be an immediate good thing that happens back? no... vice-versa for bad things...

i think it happens more on an overall collection of tendencies... i think it often manifests itself in indirect ways... meaning that if you give someone who needs money some cash you won't necessarily receive cash one day when you need it... i think it happens more like you establish a habit of generosity in life and you receive generosity someday when someone has the opportunity to sue you and they don't or something.

it also extends beyond this life... karma built up in past lives floods over into this life and karma from this life will floods over into the next. if you try to look at a single event and expect to recognize its effect is like putting a drop of water into an ocean and expecting to see a difference... does it have an effect? absolutely... just not recognizable to the naked eye.

last thought is to look at the whole picture... you were nice to a few bees one day and got stung... there was hope that your single action would have equal reaction... it didn't and that sucks! but think of all the bees and insects you have killed in your life... good thing the insect community doesn't repay you for those actions! i bet you have come out far on top with only 1 sting in thirty years!