Many people play through FFVII several tmes before seeing the real story. See... here is how iut works. Aeris is trying to SUMMON meteor herself and she is just lying about black materia doing it. Only she can hear the ancients so how would Cloud know the difference? REally White materia summons meteor and black meteor stops it. Sephiroth realizes this and tries to stop her. While she is "Praying to the planet" as she puts it she is really meditating and summoning meteor. Sephiroth tries to kill her before it is to late but he fails. Cloud is all pissed and still thinks Sephiroth is just Evil. However Clous is a dumbass and decides to go and kill Sephiroth who is the good guy (Who is still trying to get black meteria to work for him but never really manages because cloud shows up and kills him.) THe stuff that stop meteor is just snot... Snot from the planet. The Ancients were using Aeris to kill off the Humans so they could rule again.
If you don't figure this out by your 5th time playing then you are slow...
THAT IS THE REAL TRUTH!!!!!!!
Acually this is just something me and my other nerdy friend was talking about... But it is possible right? Sephiroth is always calling Cloud Ignorant And this makes him pretty ignorant to assist some chick in destroying the world...