By setting goals you give yourself mental boundaries. When you have a certain end point in mind you automatically stay away from certain distractions and stay focused towards the goal. This process happens automatically and subtly but according to research does happen. To get a better idea, imagine this. Your best friend is moving to Switzerland and his flight takes off at 9:00 PM. You leave right after work at 8:30 PM to see him off and you know it's a 20-minute walk to get to the airport. So you make it a goal to reach the airport in 15 minutes by jogging so that you can have more time to say your goodbyes. Would you get distracted by "anything" along the way? Would you stop for a break or a snack? Would you stop by your house before going to the airport? I bet you answered no for each question and at the end of the day, this is what a goal gives you. focus  No matter who you meet along the way or what you see (assuming nothing is out of the ordinary) your goal allows you to stay locked in. You subconsciously keep away from distractions and your focus remains only on the goal. And by the way if you didn't know yet this is how you become successful, you set a goal, you lock it in and then give it your 100%.