Disclaimer: Consider this disclaimed. Not mine. Neither Harry Potter nor Kelly Clarkson.

I will not make the same mistakes that you did
I will not let myself
Cause my heart so much misery
I will not break the way you did,
You fell so hard
I've learned the hard way
To never let it get that far

Because of his parents, he had never been able to be normal. Because of his parents refusing to join the most powerful man in the world, he had been forced to live with his abusive Muggle relatives. Because of his parents.

Because of you
I never stray too far from the sidewalk
Because of you
I learned to play on the safe side so I don't get hurt
Because of you
I find it hard to trust not only me, but everyone around me
Because of you
I am afraid

The man who killed them hadn't helped his situation, either. He had to hide from a raging maniac, to always be safe, to keep from getting himself killed.

I lose my way
And it's not too long before you point it out
I cannot cry
Because I know that's weakness in your eyes
I'm forced to fake
A smile, a laugh everyday of my life
My heart can't possibly break
When it wasn't even whole to start with

Dumbledore had always been too eager to point out where he was going wrong. And when he showed any sign of weakness, there was no hesitation to point it out. Everyone expected him to be happy-go-lucky, when he'd never had any reason to be.

Because of you
I never stray too far from the sidewalk
Because of you
I learned to play on the safe side so I don't get hurt
Because of you
I find it hard to trust not only me, but everyone around me
Because of you
I am afraid

But it really all came back his parents. They had decided his life for him. They had died. They had made the decision to oppose Voldemort, and, by extension, his fate had been decided.

I watched you die
I heard you cry every night in your sleep
I was so young
You should have known better than to lean on me
You never thought of anyone else
You just saw your pain
And now I cry in the middle of the night
For the same damn thing

They had forced him to grow up before he should have had to. They had died, and left the wizarding public to trust him to rescue them from the greatest Dark wizard in years. Him, a sixteen-year-old boy! It had sent him into almost suicidal depression.

Because of you
I never stray too far from the sidewalk
Because of you
I learned to play on the safe side so I don't get hurt
Because of you
I try my hardest just to forget everything
Because of you
I don't know how to let anyone else in
Because of you
I'm ashamed of my life because it's empty
Because of you
I am afraid

Because of his parents, he had never had a meaningful relationship. Because of their stupidity, his life was nothing.

Because of you

Because of his parents, he could never have a normal, meaningful life.

Because of you.

Because of them.