Concentration means control of attention. It is the ability to direct one's attention, follow one's will, focus the mind on one subject, object, or thought, and at the same time exclude every other unrelated thought, idea, feeling, and sensation from the mind.
For the majority of us, that last phase is the most difficult. Focusing means ignoring or excluding all other irrelevant thoughts, ideas, feelings, or sensations. To ignore the numbers, alarms, and other signals that indicate we have new messages, updates, "likes," or followers!
Constant interruptions reduce productivity. The task takes longer to complete. We are not as attentive. With our partners or coworkers, we don't grasp things well, leading to misunderstanding, misinterpretation, and conflict. Memory is impacted. Our personal lives and professional reputation are impacted when we forget things or have trouble recalling knowledge quickly.