Because the platform on which you are standing, that platform itself is tottering. Is tottering. You cannot make it stop tottering. This, this body . . . we have already discussed that all the miseries of our life, it is due to this body. Mātrā-sparśās tu kaunteya śītoṣṇa-sukha-duḥkha-dāḥ (BG 2.14). Mātrā-sparśās tu. All the distress and happiness that we feel in this material world, that is due to this skin, this body. Otherwise, the things as they are, they are neither miserable nor source of happiness.
The example is given: just like water. Water now, in this season, the summer season, you will find very pleasant. The same water, in the winter season, it becomes pinching. So water as it is—neither pinching nor the source of pleasure. But it is due to this body: under certain circumstances it feels pleasure, and under certain circumstances it feels distress. So pleasure and distress, these dual forms of our existence, is going on. Now, if we want to transcend above this material plane, then our . . . we'll have to completely reject the bodily conception of life. We have to stand on the spiritual consciousness of life. That is being taught.
The whole scheme of Bhagavad-gītā is like that, that we have to stand on the spiritual consciousness of life.