I always feel its when 2 sets of rules/assumptions/laws/duties collide. Both make sense in isolation, but not in tandem.
Then again, the word Paradox itself is usually mis-used, causing further confusion, which some may refer to as a paradox, which, again, proves the point further.
If one guy had mapped out life's processes, laws and ethics, there would be fewer paradox's for sure, but then paradox's occur naturally in peoples lives, so I suppose we have them because we cannot avoid them. Many are by their nature 'unavoidable'.