This happens because we always fear from getting hurt or do that extra effort and that's why our mind try to protect us. Hard things are hard. Hard things need effort to put in. It requirement commitment which most of the people don't want because of their so called other commitments which are nothing but the excuses of running away and prevent themselves from the efforts that it take. It has its own biological reasons as well which would be difficult here to explain.
The moment one feels that there would be an additional effort or there would be something that one might get hurt from, the brain sends signal to the body to stop it from happening by giving all the reasons of why you shouldn't do it. And that happens either because of our own bad experiences in the past or experiences that we have heard of.