When we first met Raiden, he was borderline cocky. He never had a real mission before, but he still thought he was a badass because of all the training he did. His girlfriend is a member of his support team, and she keeps nagging him about crap that he doesn't remember (like, "Do you remember what tomorrow is?")
After some time and a lot of failures (inability to beat bosses, supporting characters losing their lives, etc.), he starts to second guess himself a lot. Panic and fear start to take over, and the convoluted situation really get to him.
By the end, it's a major cluster of misinformation and deception, and Raiden even begins questioning the reality around him. But, by the very end, he stops trying to be the next Solid Snake and instead decides to become his own person, his own character. And that's when his character flourishes.