Sergei uses his first two wishes to wish for 1) to cure the growing cancer in his sister's lungs and 2) to cure 'Sveta's boy' (his own son) who has an ailment which the doctors think will not allow him to mentally develop beyond his age of three years. We can infer from these wishes that Sergei is a kind-hearted, humble individual who is later hardened in life by his surrounding situations, i.e. living in Russia, as the son of a Zionist etc. We know that of the three wishes that Sergei could ever be granted by the magic goldfish, he uses the first two to help those around him, with little regard for his own self or his personal aspirations.