Clinging to the material world.
Let's keep on breaking down the mechanics of our mind in order to better understand it: # 1. Our ego is the part of our mind that is in charge of protecting us, it is our survival mechanism. # 2. Our mind analyzes the world through its senses, primarily through what it can see and feel. # 3. Taking this into consideration, we may conclude that our ego will seek to protect us through what it can see and feel, and that only includes material stuff, because material stuff is what the mind can perceive. The mind can't protect you with something it cannot perceive, because it doesn't know it is there. Why is this relevant? Understanding this may get us closer to a peaceful and good life. Why can it get us closer to a peaceful and good life? Because what we described is part of the reason we are not living a peaceful and good life. Why is it part of the reason we are not living properly? By trying to protect us, our mind seeks stability in an unstable world in which the only means it has at its disposal is what it can perceive and what it can perceive is only material stuff that by essence is unstable and always changing. If we stop and think this for a moment, the material and external world (including thoughts and emotions), is always changing. Literally absolutely every moment is different. It is impossible to have two exact moments, literally exact. Absolutely everything changes. Thus, it is logical that our mind will never be able to rest because it is looking for salvation and stability in an all time changing world. What is this good for? Understanding this may get us closer to breaking our identification from our mind. The only real peace and stability can never be in the material world, it is impossible, because everything in the material world is always changing. Real stability is beyond what our mind can perceive. The twisted part of this is that we already have what we are seeking for. In fact, we are not seeking it, it is our mind and it is seeking it because it can't perceive that we have it.