It was no one other than Immanuel Kant who’s been the first to set the rule for acceptable human actions as a law for any human being:
Act only according to that maxim whereby you can at the same time will that it should become a universal law.
Nowadays people still think that some kind of role play is suitable for judging upon right actions: Try to think yourself as someone else, would you still want that action?
To become better in judging things in the right way you should consider relevant cases from time to time. Like this one:
Tough question, isn’t it?
You’re supposed to think of changing your sex and imagining a taste you normally don’t have a tiny clue of.
How good when there’s an expert to help you:
So that question is solved, don’t you think?

