Consider the following problem that might arise for an Anthropologist in the field:
In the course of conducting your fieldwork, you manage to develop very important relationships with two native informants, without whom your research would be entirely impossible. One day, these two informants extend an open invitation for you to attend a performance of their culture's main religious ritual. Although there are no restrictions placed on who may attend the ritual, you know that active participation in it is restricted to those members of the in-caste who have gone through the proper rites of initiation. The penalty for violating this taboo is never articulated - largely because only people who have been initiated into the cult ever attend - and you suspect that violating it would cause the natives to be less favorably disposed to you, and might jeopardize the rapport you have built in the community. Luckily, in the course of your prior interviews you managed to learn precisely how to go about participating in the ritual, and are confident that you could pass as a member of the in-group without incurring suspicion (note that learning the ritual does NOT mean that you have been properly initiated, which you have not).
Now, enter the problem: your two informants are of different minds as to the extent of your involvement. Both of them agree that their invitation to attend is a gesture of friendship. However, Informant A believes in the strict adherence to taboo laws, and because he knows that you are not initiated he thinks you should only be allowed to watch. Informant B, however, believes that including you and letting you participate in the ritual is an appropriate gesture of friendship - one which he feels justified in making despite the fact that it is in violation of the rules of his society.
Therefore, if you go ahead and participate in the ritual anyway, your relationship with informant A will be irreparably damaged because you're flaunting the taboo. But a refusal to participate in the ritual on those grounds will be construed as a rejection of Informant B's gesture of friendship, and will irreparably damage your relationship with Informant B. If you refuse to attend as well as participate, then you will damage your relationship with both A and B. Finally, you could also go through the process of initiation - an option which would be acceptable to both A and B - but when you ask what it would entail, you discover that it would require you to engage in behaviors that you are ethically and aesthetically opposed to, and which would set you apart as a pariah in your own society when you eventually returned from the field.
In short, you're stuck between a rock and a hard place with no way out. You either have to ruin one or both of your relationships with native informants - which would be an irrecoverable loss - or you must sacrifice your own principles and lose the respect of your own society for the sake of averting conflict with your informants.
What would you do?