A fascinating piece in The New Yorker about deciding whether to go to grad school (in English literature, in this case, but it would apply to almost any field, especially in the job-challenged humanities) mentions a recent paper by L.A. Paul and Kieran Healy on what they call "epistomological decision-making." In the case of the Paul and Healy paper, the decision-making is specifically about whether to have children (they call it "What to Expect When You're Not Expecting"). But the constraints regarding how to know if you're choosing right are much the same no matter what big life decision you're facing. The problem, according to Paul and Healy, is that the "you" who's making the long-term decision now is not the same "you" you will be after you've made the decision and tried to live with it. You can project all you want about how much you'd like to be a parent, but until you're dealing with caring for a one-year-old, or a ten-year-old, you won't really have a clue.
As they wrote
In theory, a rational choice is a series of steps: first determine the possible outcomes, and the costs and benefits associated with each one; then assign a probability to each outcome to calculate its value; finally, choose the option that gives the highest expected value. Real decisions are rarely so clean cut, because we are imperfect calculators and it is probably impossible to figure expected values with precision anyway. Yet this is the decision-making standard we aspire to. For it to work, you must at least be able to assess the costs and benefits of the most important outcomes.
But in this case, the most important outcomes include things like “what the experience will be like for me” or “what it will be like to be a parent.” If becoming a parent is a transformative experience, you can’t know in advance what it will be like for you.
Or, as New Yorker writer Joshua Rothman put it when writing about the pros and cons of getting a Ph.D.: "the decision to go to grad school in English is essentially irrational. In fact, it’s representative of a whole class of decisions that bring you face to face with the basic unknowability and uncertainty of life."
You have to make decisions like this all the time, of course, and some of the most consequential will be those you make in your twenties. But it's a fool's errand to try to make them in too calculated a way, since true rationality is just about impossible -- you can't know how you'll feel about it until long after you've chosen. You can write up all the pros and cons lists you want, but sometimes you just have to close your eyes, follow your heart, and leap.