Unresolved conflict is just conflict postponed. It will find its way to the surface in an unexpected way even if it may lay dormant for years. Unresolved conflict does not heed the rules of warfare. Peter Steinke in his book Uproar claims, “The lessening of tensions is mistaken for the resolution of conflict. Restoration of the equilibrium is not a sign that the system’s functioning is improved.”
That moment of uncomfortable animosity may have retreated and taken with it the pain caused by it, but it has not gone away. You have treated the symptom, but the root is only strengthening its attachment underneath the soil waiting to spring up and ruin your next sunny day.
If nothing changes, or no boundaries are set as a result of that suffering, you can expect it to return. A system cannot flourish built on a minefield of unresolved conflict. You have no idea what may trigger it, but I can promise you, something will.