Acharya Prashant explains that relationships do not suddenly turn toxic; rather, they are often toxic from their inception. Most relationships are founded on a utilitarian basis where individuals seek to fulfill personal needs, insecurities, or voids through another person. This exploitation is often masked by initial attraction or social conditioning. When the other person fails to fulfill these impossible internal needs, resentment and toxicity surface. The speaker emphasizes that the relationship hasn't changed over time; it has simply become more honest as life peels away the layers of personality to reveal the toxic core.