The group won't make assumptions again
“As long as it’s all of us,” Rick consoled Maggie as they drove toward the Hilltop in the Season 6 finale, “we can do anything.” We believed that: the core group has been together now for so long, and endured so much over the years, that nothing, dead or alive, is too much for them to handle. The Saviors prove that the group may not be as strong as its leaders think. Overconfidence in their abilities got Rick and the others into this mess in the first place -- had they been a little more cautious, a little more concerned with their preparedness, they might not have started this war so hastily. Going forward, you can bet our heroes will be humbled. Michonne was already cautioned; now at Rick's side, the sword-wielding survivor should exert a calming influence and keep him from acting rashly (again).