My own theory is that this is rooted in the human ancestral environment, where overconfidence was much more costly than it is today.
Blows to one’s ego are Mother Nature’s way of telling us: “Yeah, you’re not good enough.” We know this intuitively, just from how they make us feel. More specifically though, the crushing emotional defeat of a breakup serves to jar one’s sense of one’s own reproductive value down to a more realistic level. In the ancestral environment—small villages numbering no more than a few hundred people—our options were truly limited. There, it probably made sense not to be overconfident the next time. Better to pair up with someone a notch or two lower than us on the scale than to miss out entirely.
Even today, it makes sense to be sanguine about one’s prospects. However, most of us now live in a world of unprecedented opportunity. Large cities, freedom of movement, and inexpensive transportation now mean that the global village provides us with millions of options. However, we are still stuck with brains that evolved in villages. Thus, even a person living in a city of millions can feel hopeless after a breakup. (Are there data on how community size affects the pain of a breakup? It would be interesting to know how malleable this facility is.)
In short, people today usually have more options than their post-breakup emotions lead them to believe.
Concomitant with the rise of cities and easy transportation though came worldwide communication, and ubiquitous depictions of beauty, wealth, and happiness in entertainment and advertising. These ideals—much higher than the median, and out of reach for most people—cause disappointment by preventing people from setting realistic expectations.
It can be a challenge to find the right balance: to be hopeful and confident, while still setting realistic expectations.
Self-esteem comes from many sources:
- Physical health, mobility & fitness
- Engaging friendships with people we respect
- Rewarding, interesting work & the respect of our colleagues
- Fulfillment through study, practice, exercise, or hobbies
- Romantic relationships & the approval of our lovers