¹⁷The distinction between external and internal rewards, or internal and external motivation as they are called in psychology, may not always be very clear. Both come from the programmer or evolution anyway. See footnote 34 in Chapter 5 which discusses how the difference between rewards and learned state-values is not always clear; a similar logic has been applied on internal vs. external rewards by Singh et al. (2010), see also Doya and Uchibe (2005). Likewise, in the discussion of this chapter, it may not be clear if the self-evaluation system should generate a frustration signal or a negative reward signal when the long-term performance is lower than the standard required. Presumably, equivalent computations can be performed in both of those two ways. However, if we assume suffering is generated by frustration, not negative rewards per se, we have to assume the self-evaluation system generates a frustration signal, in order to explain the suffering caused by self-evaluation.