1) It's inspiring and magnetic. When you hang out with someone who is doing what you want to do you feel into their energy, their thoughts and feelings and you start to adopt the same.
2) They're a great source of advice. You don't want to take advice from on lookers who have not done what you want to do. Most likely you'll get their limited points of view. Always seek wise counsel!!!! People doing what you want to do will have a plethora of advice and information to help you on your way.
3) When you feel like it's impossible for you just watch them. They may be active on social media or you may know them personally, sometimes we need to watch someone winning at what we want to do to give us the kick up the bum we need to keep going!