Where the magic comes from is what it is.
The character of the Dubious Bastard has always been a trickster as far back as is remembered by anyone. He has always been here to show us that everything we believe to be true about nature, our belief system, the universe, and even the trickster himself is not to be trusted. He has always shown and said that we can't nor shouldn't really believe reality in general because it is all "jest a trick, pal." We search for truth and meaning when there is only chaos. We should stop trying to figure it all out because we know that no one ever has and we know that no one ever will.
Then one rainy day, the DB trickster was stuck trying to drive a car in a mind-numbing traffic jam, and he was again thinking about how Magic doesn't really exist anymore in the heart of man, nor even in his own. "There is no such thing as Magic anymore, pal, it's all jest a trick," he said to himself. "Jest a trick, pal"... no wonder he was disappointed with the time he had spent with "jest tricks..."
In the old days, when Man relied on the Earth for her kindness and bounty, in the days before the advance of the Industrialists' Rape Machines, Magic itself was strong in the heart of man and it Guided him and Protected him. Magic freed him from fear. Magic provided bountiful harvests. Magic provided freedom from want. Magic destroyed his enemies. Magic made magnificent order out of utter chaos. Magic foretold his future.
But on that day... that rainy day, as the Industrialists were flailing through their last miserable death throes and the Informationalists were struggling to take over their positions in what was left of this world's economy, as the car horns squealed and blared at each other to no avail, as the world spun through the chaos we think is our universe, as the rain fell on this rainy day... Magic let itself stand on the very edge of extinction. It looked down, and thought about its future.
And finally, after some contemplation, Magic decided to reveal itself that day as still very much alive and still very much in power.
The Trickster was relieved of his duties on that rainy day and evicted from the premises. No more would he be allowed to confuse the world with his "jest tricks." No more would he be able to cast doubts on every aspect of life. No more would he politely be permitted to challenge or undermine gentle people's belief systems.
As the truth was told, it turned out that nobody wanted him around anyway, and were really glad to see him go. Upon the trickster's eviction, he just walked away, muttering something that was never ever really understood by anyone. And that's probably just as well for all.
And there in his place, stood a Magician. And the Magician understood his powers. And he understood his position. And he understood his place. And he went forth into the new age.
Which is a good thing... or there would have been nobody to drive the car.