I have a couple of questions regarding renormalization. 1. If it is possible to change mass as long as we do it simultaneously with changing ultraviolet cutoff, that would imply that the value we pick for mass is more or less arbitrary. If so, how come we have exact decimal value of mass of an electron, which doesn't look arbitrary at all? 2. When we write renormalized mass, m=m_0+dm, we have dm >>m_0. If so, why even include m_0 at all, why not throw it out as something negligible? Thanks!