One weakness is that there is evidence that conformity to social roles is not automatic. For example, in the SPE, guard behaviour varied. There were some guards who acted sadistically, but others who were ‘good guards’. These ‘good guards’ did not harass or degrade the prisoners, and even did small favours for them. It has been argued that this shows that the guards chose how to behave, rather than automatically and blindly conforming to their social role as Zimbardo suggested.