If you go through life without any real goals, then you'll always feel like a hamster on a wheel. You feel like there is no end to what you're doing, and you'll be disinterested. Instead, define clear goals, and then work to achieve those goals. Make them small. Write down a plan, a list of items, and attach meaning to each list.
You should have large goals, and then incremental goals that give you a sense of accomplishment as well. If the road appears to be too long you'll also get disinterested. Don't focus on climbing the mountain in front of you, focus on getting to the next camp site. If you want to do 100 push ups, break that into 4 sets of 25. That's probably the easiest way to think of it. Get 25 done, then come back 5 minutes later and do another 25. Before you know it you will have done 100 push-ups and you'll realize it wasn't that bad to begin with.
Always remember: a goal without a plan is just a dream.