It is so because we are not made up of one piece. There are different parts in us, each with its own need and demand, own stage and degree of development, like different members in one family. Generally one part, the higher mind responds to a beautiful thought. It feels happy and wants to practice it. But the practice requires a strong will plus collaboration by other parts. Now if the will is weak and/or the vital elements of nature and the body is not ready then this situation arises. It is like one or two members of a family want to run to the summit of a mountain, others want to go slowly, yet others refuse because they feel it is too much labour. So what does one do? Abandon the journey? Or slowly prepare these other parts encouraging them, inspiring them through small little steps. Obviously the better option is to slowly prepare the rest of nature rather than give up the higher goals because of the pull of the lower or weaker parts.
Affectionately,
Alok Da