Hi! Im reading the book of Mathew Janda about GTo but im a little confused about a simple thing.

If we are on the river and someone bets a PSB ( pot size bet) on the river we need to defend 1/1+1= 50% to be unexplotable. And because we have 2-1 pot odds we just need to win 33% of the time to be EV 0. 

Opponent bettor: ( he is balanced with 66,7 value hands and 33,3 bluff)

When we fold : 50% of the time he is winning 1 PSB= 0,5PSB 

When we call: HE WINS 2PSB 66,7% of the time = +1.33

 and.              He lose 1 PSB 33.3%  of the time  = -0.33

So he is winning 0.5+(1.33-0.33) * 0.5= 1psb

When we call we lose 1psb 66,7% and win 2PSB 33%= 0.667psb- 0.667psb=0

I know im doing something wrong but i dont know where, if someone could explain to me would be great. 

The question is: we have to be break even only when we call or we have to win 0.5psb when call to not let him win 0.5psb when he bets and we fold??

Thanks