Why were these “poppy pockets” customarily eaten on Purim?
In my book Let Us Make Man (CIS 1987), I address the apparent paradox that a humble person is one who is actually aware of his strengths, and that feelings of inadequacy give rise to egocentricity and false pride.
However, the Hillel and Shammai academies worked together in a spirit of mutual cooperation that prevented any schism from forming in the Jewish world.
Do all that you can to express gratitude to others for anything they do for you.
(Based on Ta’amei Ha Minhagim 895.) Finally, the three corners of the hamentaschen might allude to the three-way struggle between Ahasuerus, Haman and Esther or the three Patriarchs in whose merit we were saved (Otzar Dinnim u’Minhagim, based on Midrash, Sefer Matamim Purim 2).
For a more complete treatment of this interesting topic see here.