why is string theory not on-shell, I tried many times but I was unable to understand it, the physicist said

Lubos,

it is difficult to describe the theory off-shell

a field theory is necessarily an off-shell formulation


for those who are really interested to watch this ununderstandable movie
Vanilla Sky - watch 

end minus 14:31 minutes


L'assertion est locale sur X, et on peut donc supposer X affine, donc quasi-compact et quasi-séparé