1. Question: It is explained in Bava Metzi’a 33a that if you can only save one lost object flowing down a stream or in a fire etc., either yours or your friend, yours comes first. For the verse “There shall not be a pauper among you” teaches us that your stuff comes before anyone else’s. But why is the mitzvah of returning a lost object different than any other mitzvah where we poskin that we must be willing to spend up to a fifth of our property to perform the mitzvah? The same thing should be true by the mitzvah of returning a lost object, that one should forgo his object if it’s value is less than a fifth of his entire property in order to save and give back his friends object to fulfill the mitzvah!? Why does what obligate the mitzvah of returning a lost object not trigger the obligation of spending up to a fifth but other mitzvos like tzedaka does?
A. The obligation of spending up to a fifth of one’s property to fulfill a positive mitzvah applies in a case like tzedaka where what obligates a person to give is the poverty of his friend.
B. What obligates the mitzvah of returning a lost object is the loss of Jewish money.
Answer: Loss of money is only an exemption from doing the mitzvah and by giving tzedaka for example that exemption is only applied by spending more than a fifth. But by returning a lost object which the Torah says your lost object is more important than your friends then what is obligating the mitzvah of returning the lost object is not there to require you to spend more than a fifth.