At Old Trafford on Wednesday, Manchester United surrendered a commanding two-goal lead to fall 3-2 to Brighton, becoming the first United side in half a century to collapse from such a position at home. The defeat, arriving so soon after a VAR-clouded loss to Manchester City, raises quiet but urgent questions about whether Michael Carrick — appointed to restore glory — has the depth and stability to weather the pressures of expectation. In football, as in many human endeavors, the distance between promise and unraveling can be measured in minutes.