Generally need to consider several reasons: 1, from childhood has not developed good habits of concentration, do things in two minds, resulting in difficulty concentrating; 2, long-term work or life stress, emotional anxiety, depression, impairing mental function, high stress has been shown to impair cognitive function and affect short-term memory; 3, long-term sleep deprivation, poor sleep at night for a period of time can seriously impair cognitive ability and memory; 4, long-term alcohol or drug abuse, resulting in impaired brain function and attention is affected for a long time, resulting in reduced brain efficiency; 5, anemia causes a decrease in the ability of blood to carry oxygen, the brain is relatively hypoxic, which can lead to fatigue, dizziness, thinking and concentration.