On the day Severus attended the Wolfsbane Potion review conference, Flitwick attended the deathday celebration of an old friend—Adalbert Waffling, the founder of Waffling's Law.
Waffling often corresponded with Albus Dumbledore. Minerva McGonagall passed these letters on for members of the Statute of Secrecy Special Action Group to share, including Filius Flitwick. It was through this that Waffling and Flitwick became friends.
In one of his early works, he mentioned the Theory of Conservation of Magical Transfer. Put simply, wizards and witches generated energy beyond their ability to control. That energy dispersed into the air, causing residual auras of spell energy to linger in the area. The power a wizard used to cast a spell was called the "degree of success," and it depended on the transfer and distribution of magic, which was closely tied to the wizard's emotions. The sum of successful spellcasting and the residual energy dispersed into the air equalled the amount of energy generated by the wizard.
The common mental magic Legilimency was defended against with Occlumency, which required one to control one's emotions. Harry, being so full of feeling, found it difficult to master.
Although Severus could use Expecto Patronum, the strength of his Patronus was nowhere near that of the Patronus Harry had cast in the Forbidden Forest.
If one merely wanted to cope with the courses at a seven-year full-time school of magic, there was no need to study so deeply. This theory had little to do with everyday life and could not solve emotional problems either. Before Hogwarts was founded, there had been an institution established by Queen Maeve to train wizards in learning and controlling magic. In other words, unlike a Muggle school, Hogwarts did not exist to give students diplomas and excellent report cards so they could find respectable jobs.