Rav Yosef said, "If not for this day [of Shavuos] I would be like any other Yosef in the marketplace."
Last year we discussed the Ramban, who learns from the pasuk of "pen tishkach es ha'devarim asher ra'u einecha" that there is a lav of forgetting maamad Har Sinaui. The Mishna in Avos uses that same pasuk to derive that there is a lav of forgetting Torah. How does Ramban learn the Mishna?
Achronim answer that if a person learns Torah with the understanding that this is the dvar Hashem given at Sinai, then that learning will stick with him. Forgetting Torah comes from learning without that appreciation and awareness. The lav of forgetting Torah stems from forgetting about maamad Har Sinai.
The gemara at the end of Horiyos contrasts Rabbah, who was a tremendous mechadesh, with Rav Yosef, who the gemara calls Sinai, because he remembered all the braysos and Torah shebaal peh that he studied.
The Tiferes Shlomo explains that this is what Rav Yosef meant: If not for his constant awareness of this day of maamad Har Sinai, he would not appreciate and retain Torah the way he did, and he would be like any other Yosef in the marketplace.