We humans are awful at probability. We’re even worse at logical decision-making for our own benefit.
An example is the power of a sunk cost. A person, A, dates person B for two years and finally figures that the current nature of, and likely future path of, their relationship is unsatisfactory. Person A is much more likely to reason that it’s worth staying together because of the time spent together. This is simply the way we work. That two years is the sunk cost, meaning the investment of time and energy and emotion.
A logical person would say: It matters not a whit what has transpired for me to find myself at this point. Only the future matters. The fact of my having invested time in this joint venture is irrelevant, because it’s not what I want. Now is the time to cease investing time with this person and go find a better candidate.
Instead, because we aren’t logical, we continually justify ongoing efforts to either make the relationship work, or hope that something changes to make it work. Letting go of the sunk cost appears to mean a loss, but it isn’t and never was. That time is necessary to figure out if B is in fact the right one.
To be clear: the process of getting to know someone is all about seeing how we fit together for the rest of our lives. Until we marry, it’s not a sunk cost, it’s just the cost of familiarization, and should be counted only that way.