Its not easy to stay on task when life is full of distractions. Every work day has its interruptions, crisis, questions and multiple projects. It is the way that modern business operates. Staying on task is not easy but can help you get your work done on time and ensure that your projects are completed with sufficient quality. The way in which you approach a project can make a big difference.
Distractions can be real or imaginary. Real distractions occur all the time in the workplace and are hard to avoid. If you are working on something very important you might want to consider closing your door, putting your calendar on meeting mode, or forwarding all calls to voicemail. The process will work in the short-run and for important projects but can't be used on a regular basis.
Distractions may also be imaginary. It may be equally beneficial to focus only on one project at a time. Sometimes we like to multi-task but there really isn't any proof that multi-tasking gets more work done than working on a single project at a time. Even if you only work for an hour straight before moving onto another pressing project it works out well.
Sometimes you might have two or three projects going. No one says you have to finish it all at the same time. This means you can break these projects up into hour sequences. If you get distracted you can go back and work on it again until you complete your chunk of time. If you put enough hours in you can actually complete your work.