Many couples become reactive with each other through repeated attachment injuries (injuries to the trust and attachment of the relationship). These injuries can occur from big transgressions (like affairs, internet porn, violence, lying/deception, etc). They also occur from smaller, repeated issues, like "Did s/he do what he said s/he would? Can I trust that I have a teammate in life?" The bottom line is: do I trust that my partner has my back. If the answer is "no," then we tend to build walls to protect ourselves, and attachment and intimacy reduce. If the answer is "yes," then we feel close to our partner and we tend to forgive the stylistic differences between us.