Almost everyone here has been in a situation where all they could think of was to give up. It is a natural thing and uncommon to wish ourselves comfort. It is said that the human body has limitations. This I believe means it gets to a point where the body cannot continue to function the way it is expected to. However, the most important and most ignored, the MIND, which in charge of all actions carried out has no limitations. It is from the mind that strong convictions are formed. The determination to see an activity through to the end, no matter the circumstance, exist and only a few people are able to harness that power.
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The truth will always remain the same just as it was in the beginning. It is said that until one is able to operate on a level where strength has failed and the only thing keeping one going is their WILL to succeed, nothing great can ever be achieved and I believe this. Take any work for instance, no matter how much you love doing it, it will at one point make you feel tired if you do it continuously for hours without break. What will allow you to put in some more work, knowing very well that your body needs to rest is the love you have to see the work done. I guess that is why most successful people always advice on the importance of having passion for what they do.
Everyone is capable of doing something great but only those who have developed a strong sense of obligation towards what they do can actually get it done. There is no magical powers in play, it is a WILL to succeed and that only happens when the mind is trained.