Board Thread:Questions and Answers/@comment-7708862-20130402005255/@comment-7708862-20130403165859

Ulquiorra said it: the release of power could threathen las noches existence. So the release of number 4 and higher could destroy it. Simple logic: number 4 release: threathening number 0 release: absolutely destroying las noches Because power difference is huge between up following numbers.

Also if you would use reverse logic: number 0 release: only threathens las noches then number 4's release would be harmless bcs of the power difference. (you see that the reverse logic doesn't make sense therefore the logical way is true. Ergo the release of yammi was highly contractided)