I have a question about pot

odds, concerning the mathematics behind it. Suppose that we have just seen the turn. Suppose that our equity remains fixed from this point on. Suppose also that the pot has 100 chips. Suppose that the villain always bets the full pot, no matter what. Just go with it.

Now villain bets the full pot (100 chips) as expected, so that the new pot becomes 200 chips. In that case, we need to call 100 to win 200. Our equity needs to be at least 50% in order to break even on average.

Suppose that we call, then we move on to the river. The card, we assume, does not change our equity. The villain again bets the full pot (300 chips) as expected, so that the new pot becomes 600 chips.

What equity do we need to break even? According to my own math, this should be 50% to break even from the river's point of view. However, we knew what the villain was going to do, so when we take the turn as the point of reference, then we actually need an equity of at least (100+300)/600 = ~67% to break even.

Is this right? If not, what is the mistake in my reasoning? How does this influence our decision-making?