On Harry's eighteenth birthday, when he was opening his presents he noticed another blatant sign of what he had lost when Dobby had died. He was so used to his regular gift of socks from his little friend, that when it didn't come, he felt a sharp ache in that empty part of his heart where the deaths of all his friends had ripped a hole. It had always seemed a simple thing, a little odd, out of place, but so utterly sincere, and so wholly Dobby. They were always mismatched, and knitted by Dobby himself, and now Harry felt a pang of guilt for his reluctance and embarrassment to wear the heartfelt gifts.
Socks. Such a simple thing. Such a little thing. It reminded him of what Dumbledore had told him his first year when he was trying to soften the blow of the loss of the Mirror of Erised. 'One can never have enough socks.' Now that Dobby was gone, Harry thought to himself that he could have used another pair of mismatched socks every birthday and Christmas.
Socks. Why socks? He knew they were important to Dobby, there was no doubting that. But why? Was it just because that was what Harry had first given him? Given him his freedom?
His freedom.
The sock was his freedom.
Dobby was freed from his nightmare of a life by a sock. Harry's sock. Harry's gift.
Each year on Christmas or his birthday, he would receive socks from Dobby. Dobby was trying to give him his freedom. It was the greatest gift Dobby had ever received, and he so desperately wanted to give it back.
And Harry had so needed that freedom. Freedom from the curse of the prophesy, from the endless expectations of everyone around him, from the machinations of the people vying for power, from a home with no love for him, from the haunting shadow of Voldemort.
Dobby had seen Harry's need for freedom and tried to give it to him the only way he knew how.
The next day, Harry took out one of the pairs of socks he had received from Dobby and pulled them on. He looked down at his feet, a smile struggling to grace his lips, and his throat choking up. He would not cry. There was nothing sad about this gift. It was a gift from a true friend, one he would remember forever.
As he slipped his feet into his shoes he remembered Dobby's final gift. He had rescued them from the snake pit, and bought their freedom with his life. Harry stood, and strode out the door, freedom on his feet.