Understanding - the first step to acceptance ~ Dumbledore

"Karkaroff?" said Moody with an odd laugh. "Karkaroff fled tonight, when he felt the Dark Mark burn upon his arm. He betrayed too many faithful supporters of the Dark Lord to wish to meet them... but I doubt he will get far. The Dark Lord has ways of tracking his enemies."
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"I was patrolling around it, able to see through the outer hedges, able to curse many obstacles out of your way. I Stunned Fleur Delacour as she passed. I put the Imperius Curse on Krum, so that he would finish
Diggory and leave your path to the cup clear."
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At that moment, Harry fully understood for the first time why people said Dumbledore was the only wizard Voldemort had ever feared.
The look upon Dumbledore's face as he stared down at the unconscious form of Mad-Eye Moody was more terrible than Harry could have ever imagined. There was no benign smile upon Dumbledore's face, no twinkle in the eyes behind the spectacles. There was cold fury in every line of the ancient face; a sense of power radiated from Dumbledore as though he were giving off burning heat.
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"Come along, Potter," she whispered. The thin line of her mouth was twitching as though she was about to cry.
"Come along…hospital wing…"
"No," said Dumbledore sharply.
"Dumbledore, he ought to - look at him - he's been through enough tonight -"
"He will stay, Minerva, because he needs to understand," said Dumbledore curtly.
"Understanding is the first step to acceptance, and only with acceptance can there be recovery. He needs to know who has put him through the ordeal he has suffered tonight, and why,"

~ Veritaserum