פירוש על בבא מציעא 42:2

That he ultimately despairs (abandons it) - after this one finds it. And the principle of abandonment is such as when he says, "Woe is me for the monetary loss" - as he reveals his thinking that he has despaired about [reclaiming] them.

Because when it fell, he does not despair (abandon it) - And even though, he abandons it now, it is a general coincidence; and he was not prepared to abandon them as first.

In a prohibited [manner] that it came into his possession - For it is something that is not prone to be abandoned.