The best way to start something is to take a cue from Nike and just do it. But ending things is much trickier; either we end things too soon and regret it afterwards, or take to long to end them --which makes it more difficult to do so. To avoid the former, dig in your heels a bit longer. The easiest way to tell whether or not you're ending something too soon is to ask yourself whether you really started.
My father started a youth program at my mosque. After the sermon was over, he would conduct a discussion with the kids and teens. The topics weren't about religion so much as it was about our values and ethics. When is it OK to lie? Who are you? No one in the discussion had ever been asked those questions before, and as the discussions went on it became something that members looked forward to. However, us members wouldn't have that program if my father listened to other people and pulled the plug on the program after the first meeting, or before any meeting, really. People tend to resist change, and the adults at the mosque weren't in favor of adding a youth program. They didn't see the point of it, at least at first.
After a few months had gone by, parents were calling my father commending him for the program. They noticed a change in their children. Kids who were shy gained confidence. Others learned how to listen to someone else's opinion. These are changes that take time and effort to happen. While the group eventually came to look forward to discussions and enjoyed having them, at first getting kids to participate was like pulling teeth. Kids are shy, so it takes time for them to get comfortable.
Beginning anything new will be met with resistance, either from you or from others. The first few days at the gym leave you feeling more sweaty and sore than fit. The first date starts off more awkward than romantic. And learning a new skill is frustrating. But it gets better. Be patient with yourself, and with others if they're involved. Approach your new venture with increasing determination. Never forget why you started it in the first place, or what you stand to gain if you continue.
But what happens when you're past the beginning and at your wits end? We like to put time constraints in our lives: go to high school for four years, earn undergraduate degree in four years, spend a gap year abroad, etc. Point being, we are used to (and like) the idea that there is a set duration for which things happen and which things come to an end. That's why it's especially hard to confront the end of something for which we anticipated no end.
A few years ago, my father wanted to open up a restaurant. He had never even worked in a restaurant before, but of course that didn't stop him from diving into it full force, like he does with every venture he sets his heart to. For over two years, he poured his all into trying to make his vision become a reality. He renovated a store in Queens, hired the employees, jumped through all the legal hoops, and in the end it just couldn't work out. After two years, he couldn't find a manager and saw that the restaurant still needed more investments, ones that he could no longer give.
When we talk about how difficult it is to end things, it's usually about relationships, not restaurants, but the same principle applies. Firstly, put your all into it. If after time the relationship needs more investments, ones you cannot give and probably wouldn't yield results anyway, decide to end it. Making the decision is the hardest part. You've invested so much time, so much of yourself, into the relationship. How do you end it? Well, what if you already ended it? If you've given up trying to make things work and don't believe it will get better, then the relationship did end, just not officially. How do you officially end it? The particulars of that are up to you, but once you've settled on a course of action follow it through.
The worst thing to do is to not make a decision. You haven't given up, but your heart's not in it either. Personally, I don't see a point in that. Time is precious, and the time spent half heartedly in one place would be much better spent whole heartedly in another. Also, when you give up, it's not as though you can never come back to it, at least not always. My mother ended a friendship a little less than twenty years ago, but met up with her friend again a few months ago. I wouldn't say that the relationship started over, but it started anew. Things were different, but maybe things need to be different for something to start again. 
However, most of the time, we don't get to decide when something ends, it just does. Other times, we want something to end but it just won't. In those cases, we have but one option, to continue on until we reach the end or a new beginning.
