How to Improve Cooperation - Try a Double Dose of Assertive Humility
From HBR: To Collaborate More, Try an Olive Branch on Steroids
With the exception of “dyed-in-the-wool” unforgiving types (you know, the ones who seem to delight in ruining family holiday dinners), one of the things that nearly the rest of all other people are defenseless against is a sincere, earnest, unsolicited apology.