Although I firmly belong to the group of fans who like their Loki dark and twisted (as opposed to 'misunderstood') I found
this piece on him interesting.
Right or wrong, beliefs and perceptions motivate any action. It's hard to not act differently if other beliefs or perceptions don't occur to you, if they're outside of your realm of experience, if they contradict your own to the point where you'd have to reinvent yourself to change your mind, or if you simply can't grasp them. We wouldn't expect a computer to act differently than it's programmed to, right? And the brain is a supercomputer programmed by a mix of chemicals and outside influences. We may still be responsible for our choices, but overcoming programing's not an easy thing -- especially if it doesn't even occur to one to question it (and even more especially if the computer is faulty).
Loki was raised to believe he was a king, and raised on stories of how his father conquered the Jotuns. These were key points that immensely informed who he was. What kind of number must it have done on his self-esteem, then, to see his reckless brother about to be named king when Loki perceived himself as more capable of the job? Then he discovered he wasn't even a member of the family, and so by simple virtue of his birth was never going to be "good enough."