qui gonn not disapearing

Why did Qui-Gon even die? He certainly didn't just decide to like Obi-Wan and Yoda. I'm sure he didn't want to. This may be it--He wasn't planning his death disappearance because he didn't expect to die. Also: Was he angry, turning to the dark side? We already know he was a rebel to the Jedi Council. I'm sure he didn't in that split second turn to the dark side, but maybe he was having agressive feelings, and so couldn't die like a true Jedi Master. Also: how did Obi-Wan become more powerful? By directing Luke, who had more physical power and could get around better. Also: both Yoda and OWK were old, and QGJ was not. Maybe they collected enough of the force inside themselves that it sort of filled and absorbed their bodies when they died and carried their images on. Yeah, some mystical thing like that. Of course that doesn't quite work with Vader . . . I'm just brainstorming here, fishing for ideas, you know. My only claim to knowledge is I've seen the movies and have a brain. I haven't done any espionage/research. Elanor