What happens if you take a coat to shul and when you come out your coat, it is not there, but a another coat just like it is? Are you allowed to take that coat or not?
Rav Yisroel Yaakov Fisher (Even Yisroel 8:96) says that you may take the other coat for two reasons. Firstly, if you are not sure it is yours because it does not have a siman, there is halachic grounds to assume that it is yours, because you left one there just like. it. Secondly, he says, even if you know it is not yours, you may still take it because the real owner, who took your coat by accident, wants to let you use it so that you will let him use yours.
He brings a raya from the Mishna in Succah which says that when the first day of Succos came out on Shabbos, everyone would bring their lulavim on Erev Shabbos to the Har Habayis. The next morning, the gaba’im would throw them to the crowd. Everybody would grab a lulav and each person was mochel the person who took theirs, granting their lulav to him bematana. This way they are yotzei with a lulav that halachicaly belongs to them.