The real reason you can't focus has to do with these five elements. Ensure you understand these elements and utilize them to your advantage to recapture your focus and become more productive.
This one might be obvious but it also may be most important. Your brain can't focus without energy. To regain energy you need to take breaks, get enough sleep, and eat regularly.
Often ignored or taken for granted, your emotional state drives the quality of your focus and the results you can achieve. If you work in a fear-driven organization that is low on trust, your performance will understandably suffer. The better you understand yourself, and your emotions, the better you will be able to keep yourself in the best emotional state to focus.
You must be interested in order to pay close attention. You must also be motivated. Interest and motivation equal engagement and care. Lack of caring in the work you do will lead to a lack in productivity.