Plain old vanity (specifically, intellectual pride), pedantry, a lack of neighborly love, a wish to dominate others (libido dominandi), pettiness, pusillanimity, and insecurity. Magnanimous people do not feel the need to flaunt, certainly not in the faces of beginners. They are generous, patient, and gentle with those who know less. They desire the good of the other in sharing what they know.

I am reminded of the most common reading at wedding masses, 1 Cor 13 [0].

[0] https://www.bible.com/bible/59/1CO.13.ESV