The gaon Rav Yechiel Michel Feinstein [Rav Moshe's nephew and Rav Yitzchak Zeev Soloveitchik's son in law] once made a siyum on maseches Zevachim and was especially happy. He was asked why he was so happy. It was the first time he had finished Zevachim?
He said that in the past he learned Zevachim but didn't learn דף ל. The talmidim pointed out that he gave shiurim on דף ל in the past so of course he had learned it. He replied that yes, he "said Torah" on דף ל but hadn't REALLY learned it. He remembers when Rav Chaim "Stutchiner" [Shmuelevitz ztz"l] was in the Mir and stood opposite the wall and reviewed דף ל about 40 times until everything became clear to him. He [R' Yechiel Michel] also had learned many other pages from the maseches but didn't have the same "geshmack" from דף ל. This time however, he felt the "geshmack".
That is why he was so overjoyed.
אין זכייה כתורה.
[Yeshurun 14 page 311]