Hal yang Tidak Diketahui Saat Belajar di Filsafat

weeks ago i got question on filsafat exam. the lecture asked us what thing that we wont know even we have learned it on filsafat. well it took a long time ti think bout it. till now, i haven't found the answer. i think maybe it was heart. because noone know how deep someone's heart. cmiiw. i hope ill get the answer soon :)