Why do some shy, insecure women flee when they find out their crush likes them back?

Why do some shy, insecure women flee when they find out their crush likes them back?
Life has built-in programming: seek pleasure/comfort/safety, and avoid pain.

Most shy women are nervous and guarded when they're uncertain if a guy likes them, but are thrilled and relax a lot when they find out the guy likes her.

How does the rule "avoid pain, seek pleasure" apply, with women seem to lack confidence (who are likely very shy and insecure): who pursue when they're unsure whether the guy is into them, but flee when they find out he likes them back?
Why do some shy, insecure women flee when they find out their crush likes them back?
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