Why do we resist the things we intellectually know are good for us or that we should do like physical exercise zazen healthy food and do other shallower activities instead tv social media ....

Everyone is like this. It is the three poisons, greed hate and delusion that make us act this way. We are easily unbalanced, either not feeling inclined to do things, or then doing things excessively. We as humans have this unclarity of mind, we cannot see through and beyond the things right in front of us. Yet if we suffer or if we feel danger, then we can move. That is why we need to bring light to the unclarity, we need to be able to look far ahead in our life, and to move accordingly is called wisdom. Depending on how quiet our mind is, can we make the right and serene decisions. Through the practice of Zazen we can bring the light of wisdom to these unclear places within.