Why do we desire something that is always hard to get?

I read an article from magazine today talked about how people's brains would produce 'Dopamine' when people craved for something they wanted. This chemical from brain would excite people to focus on hunting down their goals. Moreover, when some barriers occured keeping people from reaching their goals, brains would release more 'Dopamine' and which would enhance people's concentration on thier goal-huntings! This articale ended up with a conclusion explained why some women always craved for men that were already in relationships and vice versa, men were like that as well~

An object that is hard to get but makes people craving to death~~

I am thinking, could this craving for something or someone that is hard to get , merely be the curiosity of people?
The objects that arouse people's curiosity, but the feeling be mistakenly taken as the attraction?
So, for those who desire other people's BFs or GFs; could they only feel curious about other people's seem-to-be-good partners, but be attracted to?

It is quite possible because according to the ariticle, it mentioned that when the 'Desire' took place, brain would become irrational to keep people away from considering the realistic aspect. Since the chemical would make your brain superfocus on the things you are pursuing! It blinds the practical aspects of things that could be obvious to observe around you.

People get confused with their curiosity to the feeling of attraction that could produce something else such as lust and love.

I am haunted by this question my friend gave me. Still seeking an answer to it~~~ Not yet knowing a better way to put it down it words!

(Oh! Why do I always need more time to express myself in words?)