How come i can get an orgasm just by thinking?

simply this you know what you like & enjoy

because you're lucky

Some people can, most people can't. It is especially difficult for us guys. When I was 12, I managed to 'think' my way to orgasm just once. I have tried it many times since, but that was the only time it worked.

A lot of women, maybe most, are very "hooked up" - most of their bodies are erogenous zones. They are very sexually sensitive and, depending on the individual, may orgasm from touching and stroking in most areas, simply pressure and kissing in some, breast feeding, and aural and visual stimuli such as listening to music (my first wife got off to Wagner's Prelude and Liebestod from Tristan and Isolde), looking at billboards, pictures, or men. And, as you say, some can think themselves into orgasms when they want to or are in the proper mood.
The answer to your question is that you are very sexually sensitive and responsive.

My answer would depend on your gender. If you are male, I'd say you are a rare bird, unique amongst humans.

If you are female, you may be oversexed, but it seems that many women can bring themselves to a certain level of sexual excitement by imagining that they are making love. Women are more sensitive to sexual stimuli than men, for all their sexuality is internal, including the physical equipment. I've known several women whom I could bring to orgasm simply by talking to them. One girl got a wet spot on the crotch of her jeans from listening to me rehearse a perfume commercial. Another girl, I talked to her nipples on the phone. She said they got so hard that they stung. She was panting when she said it.

Once I was in a IM chat with a woman, and I described, in the present tense, how I would make love to her. Her responses were things like, "Oh, Yes. Go on," and "God, I love that." After some 20 minutes of chat, increasing in intensity and sexual imagery, she wrote, "Oh My God! You just gave ma an orgasm; something my husband has never been able to do in six years of marriage."