How could Rebbi Zeira forcibly forget his learning?

Question

In Bava Metzia 85a it says that

ר' זירא כי סליק לארעא דישראל יתיב מאה תעניתא דלשתכח גמרא בבלאה מיניה

Rebbi Zeira, when he left to the land of Israel, fasted 100 times to cause himself to forget the Babylonian talmud.

How was this allowed given that the mishnah in avos 3:8 says that anyone who forcibly forgets his torah learning is culpable for his life?

Answer 1

The Lubavitcher Rebbe explains that there are three opinions as to what "Pen Tishkach" prohibits:

1. Rambam doesn't count it as a Mitzva at all. Moreover, according to the Rambam, one doesn't have to learn Svara, just the final Halacha, so forgetting Bavli would be fine.
2. Ramban says it refers to the giving of the Torah, and the Drash in Avos is an Asmachta and is only a Chumra.
3. Smag says that one only violates that commandment when one doesn't spend time learning, and he probably spent time learning other things (in other words, it's prohibited as a form of Bitul Torah).

Answer 2

The Baal HaTanya, in his introduction to his Shaar HaYichud V'Emunah, talk about this idea with regards to the verse in Mishlei 24:16, "For a righteous man can fall seven times and rise".

There he explains that when a Tzaddik advances from one level to another, "Between one level and the next, before he can reach the higher one, he is in a state of decline from his previous level"

The Lessons in Tanya further elaborates:

When one is constantly on the same level, or even when one advances in finite stages from one comparable level to the next, there is no need to abandon one’s former level before establishing one’s foothold on the next; on the contrary, one’s former position may well help one to take the next step upward. When one is truly mobile, however, climbing from one level to an infinitely higher one, his previous level — which is finite compared to the level he is about to attain — actually hinders his progress. Indeed, if he aspires to mature to a more exalted spiritual mindset, he must first purge himself of his previous one.

In a footnote, the Lubavitcher Rebbe explicitly connects this to R' Zeira.

---

In a Sicha from 6th of Adar, 1980. The Lubavitcher Rebbe interprets it as follows (see there for context):

R. Zeira did not literally forget Talmud Bavli. It was just that this intermission (the period of fasting), compared to the actual learning done previously, is called “forgetting.” And it was precisely this “forgetting” which was necessary to reach the higher level of Talmud Yerushalmi

Answer 3

Steinsaltz's commentary to Bava Metzia 85a provides a great explanation as to how to read this gemara:
(English translation adapted from Sefaria)

מלהגיע לדרך הלימוד של ארץ ישראל, שכיון ששיטת הלימוד שונה שם ולא רצה שיבלבל אותו לימודו הקודם ...

... so that it would not hinder him from adapting to the unique style of study prevalent in Eretz Yisrael, and he didn't want to get confused by his previous method of learning [eg: his method for learning the Babylonian Talmud]

Rebbi Zeira didn't chas v'shalom forget THE KNOWLEDGE of the Babylonian Talmud, he forgot THE METHOD used to learn the Babylonian Talmud.

Answer 4

It's the same as yosef forgetting his family when he names his son menashe. He wasn't forgetting information, as per Mishna. He had to forget darkness in order to learn light.