The properties of quantum space are similar to thermodynamics. That is, the property of quantum mass m is the same as pressure P. Therefore, the combination of 1 eV and 9 eV in quantum space is not addition 1 + 9 = 10 eV or middle 10/2 eV, but multiplication 1 x 9 = 9 eV or square root √9 eV. The core of Koide formula is to figure out what the root mass means. The key points are as follows. (1) Origin particles are 3 neutrinos and 3 gravitons (graviton, photon, gluon). (2) The 6 origin particles exist all in electron, muon, and tau. (3) The compressed quantum space is reversible and optimized. As the result, the √m is established. (4) The 9 combination mass regions are composed of 3 mass regions of electron, muon, tau and 6 empty regions. (5) Electron, muon, and tau fight each other to occupy the six empty regions. The fighting process is 1/3 < Koide value K < 1. (6) The fairest and most stable result of the fighting is 2/3. From this, it can be understood that quantum space was reversible and optimized before Big Bang. The K is calculated as 0.666 661(7). The anomalous magnetic moments at the g-2 factors of electron, muon, and tau affect Koide formula very finely. Considering this, the value is calculated as 0.6666665. The K is judged to be 2/3 correct, and the mass of tau is predicted to be 1776.8885 MeV.