In a world where names have a certain kind of spiritual power, Dean has several different encounters with the phenomenom.
All of them are life changing.

I'm sorry for the formating, FFnet is being a bitch once again and deleting all my breaks and paragraphs, hence the ugly lines. Check out the AO3 version for proper formatting-.-

What's in a name? that which we call a rose

By any other name would smell as sweet;"

- William Shakespeare, Romeo and Juliet, Act II, Scene II

When Dean was still a toddler and had only started to produce his first words, his mother told him about the importance of names. "Names", she said, "have the power to change things. Remember to never carelessly name something." She was so serious while explaining this, that Dean, not understanding why she was speaking to him in such a way, started to cry. But it left an impression in him and when his little brother Sam arrived, he chose his name with care.

The name he gave him remained the same over the years, even when Sam left them.

The day before Dean was to start elementary school, his father took him aside. What followed was a most memorable conversation for Dean. "Son, your mother told you how important it is to name things the right way", his father started. "Thus, you know that you cannot name anyone at school. Use their names and play with them, but never name them. It will only bring you heartbreak when we have to move again." It was the only time that his father spoke about such things with him and Dean followed his father's advice.

Throughout his school years he talked to people, was charming, flirted with some of them and slept with others, but never did he name one of them.

The month Dean came to the conclusion that he had to be in love with the girl, he was stunned. He couldn't deny that what he felt for her had to be love and at some point he named her. When they had to move again because his father had gotten news of a new monster to hunt, Dean was devastated. Only when his mother had died, he had felt the same kind of headache. "Believe me", Bobby had advised him later, "it's easier if you don't do it."

And Dean had known what it was and stuck with that.

The year his father allowed him to drive the Impala for the first time, Dean was exhilarated. For years, the Impala had been what he considered his home, but the moment Dean touched the steering wheel and felt the fabric beneath his fingers, he named it thus. They were always on the move, driving across the country from one end to other in order to chase down what had killed his mother. Never did they stay at a place longer than a few weeks, or very seldom months, but the Impala was always there. It was the only real, unchanging constant he knew. And when he overheard Pastor Jim say: "It's really a shame that they will never know a real home.", Dean thought nothing of it because the Impala was all that incorporated home.

The night Jessica died, Dean saw for the second time what kind of an impact the loss of a person one had named had. Losing a person to death was different from losing a person because one had to move. And then and there, seeing his brother's breakdown, Dean felt so very lucky, that he had followed through with his policy of not naming anyone apart from his family. It might have rendered him somewhat cold towards others, but at least he would never have to suffer through the pain he had seen in his father and his brother. And when his brother screamed at him: "You don't know anything, Dean. You never let anyone in.", Dean didn't feel hurt, but strengthened.

He didn't need anyone as long as he had his family and when the hellhound got to him, he found relief in that thought.

The second the being that called itself Castiel showed him his wings, Dean named it. It was a subconscious decision and exactly the kind of thing his mother had warned him about all those years ago. Names had power and once you named something, it was part of you. "I'm the one who gripped you tight and raised you from perdition", Castiel claimed and at that moment Dean knew it for sure.

When he told Ellen about it at some point, the only thing he got was a chuckle and a "Men". Castiel, though, remained 'angel', even during times he was not on Dean's side and later when he lost his grace.

Because the heart only names once.