I recently answered a question and the answer was awarded $35$ points. A few days later $15$ points were deducted. What sort of mechanism determines the number of points in the first place and where did the subsequent deduction come from?
The questioner had accepted your answer, giving you +15 (in addition to the 2 time +10 from the two upvotes).
Yet, they then unaccepted your answer to accept another one. This deducted the +15.