Stealing Somebody Else's Mitzvah
Q. I recently did a kindness for someone. But someone else wanted to do the same kindness, and felt hurt that he was now unable to help. Am I required to forgo an opportunity to do help when I know that someone else would like to do it instead?
A. I think we're in good shape when we are competing over mitzvot (good deeds), and not the petty and unimportant things that people are usually fighting over.
But precisely because Jewish tradition recognizes the transcendent value of good deeds, it also recognizes that we have to be equitable in allocating them. According to Jewish law, it is forbidden to "steal" someone else's mitzvah. The Rabbinical court can even impose a fine on someone when they deprive the "owner" of an opportunity to fulfill a commandment!
So we see that the ability to do a mitzvah is very valuable, so valuable that if someone is deprived of this ability he deserves recompense. But actually the mitzvah is even more valuable than this. Here is the explanation of Rabbi Yechiel Weinberg, a leading Rabbi of the last generation. "The fine of ten gold pieces is not a recompense for the stolen mitzvah. For who can even begin to assess the reward for a mitzvah? Rather, the fine is for the sorrow which he caused his fellow, for every person is upset at having lost the opportunity to perform a good deed."
We learn from Rabbi Weinberg that the ability to do a mitzvah is invaluable. And we also see that every person, not only an especially pious one, has a powerful desire to do right and help others.
This doesn't necessarily mean that you did something wrong. The mitzvah is not "stolen" unless there is some objective indication that the person actually "owns" it. For instance, the father is responsible for circumcising the son. So if someone else takes the baby and performs the circumcision, then the father has been deprived. A shochet (ritual slaughterer) is responsible for covering the blood of the animal, so if someone else fulfills this mitzvah, then the shochet has been deprived.
In your case, it may be appropriate for you to forego a kindness if you know that it is primarily someone else's responsibility. If you are first in line but you know that someone else would really like to do the mitzva, then you are in an admirable position. You can choose between two mitzvot: helping the person in need by doing the mitzvah or helping the second person by allowing him to perform it in your place!
SOURCES: Babylonian Talmud, Bava Kamma 91b; Shulchan Aruch Choshen Mishpat 382; Responsa Seridei Esh III:96.