I guess I will have the zechus of opening the Sukkah Forum.
So yes, I decided to start doing daf Hayomi again and the shiur that I am attending has already started Sukkah.
The Gemara 2A gives 3 reasons why a Sukkah higher than 20 Amos is Pasul.
(1) Rabah - One can not see the shechach (Lo shalta beiy eyna) and is therefore not aware that he is in a Sukkah.
(2) Rav Zeira - One is not sitting in the shade of the Sukkah
(3) Rovo - A Sukkah has to be a temporary dwelling (or at least able to be temporary)
There are differences between these 3 opinions as the gemara explains on page 2B. Basically according to the third opinion there is no Sukkah which will be kosher when higher than 20 Amos.
According to the other opinions there will be certain situations when it will be Kosher even when higher than 20 Amos. [if the walls reach the shekach (1st reason) or if the sukkah is bigger than 4x4 Amot (2nd reason)]
Lehalacha The Tur and Shulchan Aruch, as well as he Noisey Keili Pasken like Rovo and therefore all Sukkahs higher than 20 Amot are Pasul.
It's interesting because as a school child (one is always taught that the reason why the Sukkah is passul when higher than 20 Amot is because of Rabahs reason that one can not see the sechach, when in fact lehalacha we do not pasken like Rabah.
Go ask a random guy why a sukkah higher than 20 Amot is passul and more times than not he will answer because of 'lo shalta beiy eyna' that one is not aware that he is in the sukkah - Rabah's reason.
Incidentally by Chanukah and by Korah (eruvin) then everyone will agree that the reason why they are passul when higher than 20 Amot is because of 'lo shalta beiy eyna - not being able to see the chanuka lights or korah".
Maybe this is how the mistake became widespread with regards to Sukkah. (Since it is in fact the only reason why other things are indeed passul when higher than 20 Amot)