In answer to the OP, in my interpretation of what's on screen, Qui-Gon's consciousness does form itself from the "Netherworld of the Force" until Anakin's first steps towards the dark side (when he slaughters the tribe of Sand People). So you could say that that action "caused" Qui-Gon's spirit to form. One way of seeing it, then, is that Anakin's first steps towards the dark side also contained the seeds of his redemption. I think the idea is that people can only communicate with Force ghosts they've actually known in their lives. The Force ghosts don't really exist "in reality," (which is why nobody seems the three Force ghosts at the end of ROTJ except for Luke) they just exist in the mind. IMO, the metaphor for that scene is that those who've taught us in some way don't really ever leave us. So from that point of view, Qui-Gon *shouldn't* be there.