Why does the benzene ring shifts ?

In benzene molecule(C₆H₆),all six carbon atoms are sp^₂ hybridised.Two sp² hybrid orbitals of each C-atom overlap with sp² hybrid orbitals of adjacent C-atoms to form six C-C sigma bonds which are in the hexagonal plane.The remaining sp² hybrid orbital of each C-atom overlaps with s-orbital of a hydrogen atom to form six C-H sigma bonds.Now one unhybridised p-orbital of each C-atom are close enough to form pi-bond by lateral overlap.There are two equal possibilities of forming three pi-bonds by overlap of p-orbitals of C_1-C_2,C_3-C₄,C_5-C₆ or C_2-C_3,C₄-C₅,C₆-C₁ respectively.The six pi-electrons are thus delocalised and can move freely about the six carbon nuclei.The presence of such delocalised pi-electrons accounts for the shifting of benzene ring.