One of the few times I tuned into what the philosophy teacher was saying in his lecture I heard him speak of a theory on happiness. Of course it grabbed my attention as my angsty self believes that happiness is an illusion.
Here's what he talked about: pure bliss, happiness is felt when an individual is fully engaged in an activity that has challenges equivalent to the individual's abilities. That also get harder and instant rewards or gratification is granted from the surpassment of the challenges. This is why video games are so popular.
But also this is why long term goals are so hard to achieve. The lack of any sign of remarkable progress slowly but surely kills the motivation and the hype with which one starts off with. So it's not about whether you are strong and capable of exercising daily, eating healthy or stopping smoking it's a matter of having faith that what you are doing is actually worth it. And the best way to do that is to extensively research about the thing you want to achieve in order to make yourself believe that you can't live without this. Want to give up sugar? Yes sugar is bad, everybody knows that. But taking some extra time to research how it blocks leptin and makes you overeat can freak you out next time you mindlessly reach for 3rd piece of pie. Can't stop smoking? Talk to former smokers, get a glimpse into their personal hell. Not motivated to learn a foreign language you are interested in? Go watch a movie in that language, feel the beauty of it and the agitation of you not knowing it yet.
You need to get scared. Scared that you will miss out on the benefits of your goal all because you couldn't speculate the immediate results. You need to get it engraved in your mind how much you will miss out on if you don't start doing what you want to do. But most importantly, have faith that your goal is in fact worthwhile and understand why that is so. Plus, the more you do something, the more enjoyable and easier it gets, so the hardest part is starting.
Also I want to end this with an insightful quote from the play Ros and Guil "we cross bridges when we come to them and burn them behind us, with nothing to show for our progress except a memory of the smell of smoke and a presumption that our eyes once watered". Meaning that if you want to get into shape but you rather take a nap than go for a run REMEMBER that in the long run (haha that wasn't even intentional) you will only have the memory that you enjoyed your nap adding nothing to your progress, but if you do run you will in fact burn some kilojoules, unfortunately, you might not see those calves popping right away. But remember that with persistence they will be popping, believe in your calves and have faith in the greater good that your achieved goal will bring to you.