A study shows that employees who are often encouraged by praise and other spirits are 25% more productive than employees who are rarely praised, and the objective criteria for evaluating production efficiency include the number of contractors and the complexity of the workpiece. This shows that more spirit Encouraging can increase employee productivity. Which of the following, if true, would most weaken the conclusion? ['Commendation is actually the spiritual reward for highly productive employees.', 'Objective criteria for evaluating production efficiency should also include the quality of the workpiece.', 'Spiritual encouragement sometimes causes employees to have blind self-confidence and a false sense of achievement.', 'Low productivity employees have less working hours per day than high productivity employees.']