Can someone help me with a formula Trying to wrap my head around the whole idea behind the frequency in which I would need villain to fold given my bet size in order to make an immediate profit and of course inversely how much I would need to be calling in order to stop my opponent from making an immediate profit.

There's something I'm not understanding and was wondering if I can get someone to elaborate on what it is I'm missing. I'll explain what I'm talking about in the following example:

Suppose we are on the river and I make a pot sized bet. I need Villain to fold 50% of the time for me to "break even" given my bet size amount. However, for villain, I am laying him 2 to 1 and thus he only needs to call 33% of the time for him not to get exploited.
I don't understand why these percentages don't match. What am I not seeing here?
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