It was true that Professor Baker had handed Avada his complete method for learning his trump card, Dual Casting. And after removing the Trace from his wand over the summer, Avada had indeed managed to squeeze in some practice. In the final few days of summer, he'd even succeeded once...
Then he realized that, at his current level, the technique was basically useless.
From the perspective of natural ability, the structure of a normal human's brain and mind simply didn't allow for genuine parallel thinking. A person could only focus on one thing at a time; so-called "multitasking" was achieved by rapidly switching between thoughts. But casting a spell was a process that couldn't be interrupted. That was why, since time immemorial, there had never been a wizard who could truly cast two different spells at the same time.
And yet Professor Baker was an extraordinary talent. Somehow, he'd hit upon an idea and painstakingly worked out a method that perfectly bypassed the mind's limitations, achieving true "multitasking" through what was practically a loophole in the system.
However, this method came with severe restrictions and side effects.
First, it was incredibly difficult to master; even the slightest mistake would cause it to fail. Even though Avada could directly see magic, he'd still failed countless times before managing a success.
Second, it consumed an enormous amount of energy. Avada had no idea how Professor Baker had managed to endure it, but on the night of his first successful attempt at Dual Casting, he slept for fifteen hours straight—and still felt groggy when he woke up the next day.
And then, combining the first two drawbacks gave rise to a third: while using Dual Casting, it was basically impossible to cast high-powered or even slightly complex spells.
That made sense. A person