Why is the problem with the personal pronouns 'I, me and mine'? 9 Attitudes of mindfulness - Jon Kabat Zinn 

Jon describes these pronouns as problematic because who we actually are is far greater than that. How so? Please detail why the problem lies with the personal pronouns 'I, me and mine'.
Begin with these 3 characteristics which are true of all things: 


impermanence (also called change): nothing ever stays in one state or eternally the same. Use things like flowing rivers and growing plants, or the effects of time/gravity/erosion to visualize this constant growth, decay, transformation, evolution.  
unsatisfactoriness: although we may feel for brief moments that some things are "perfect" (wonderful), we quickly begin to realize that there are imperfections, flaws, difficulties, and obstacles in all things/situations.   
non-self (also called unsubstantiallity):   


When you refer to something as "mine" you are labeling it as something stable and unchanging. That's nicca (permanence). But it is truer to say that it is momentarily (at best) "yours", because your hold on it is impermanent. Even (as an example) if you call land "yours" it was there for an unmeasurable time before you arrived, and it will outlast you by an even greater period of time. It is also changing constantly, and it is unaware of you.  

A human is the sum of : 
1. Body, 
2. Feelings, 
3. Perception, 
4. Thoughts/Mental Formations, 
5. Consciousness. 

I numbered them because you will often hear them referred to as “5 aggregates” that means that everything you can list about your ‘self’ can be put into one of these 5 categories.
Although you may feel that each of them are solidly “you” if you take a little time you will begin to see that all of them are constantly changing. For example, your thoughts feel as though they are “you”, but just because you had a negative thought doesn't mean that's who you are. You are not that thought, and it is not you. 
Observing these 5 parts of “you” changing during meditation will help you achieve the understanding of their impermanence. Buddhism is mainly concerned with experiential knowledge and through meditation you may achieve this insight.  The practice of mediation is where the conviction of non-self (anatta) grows. These 5 are always changing in response to continuously changing conditions and this makes them unsubstantial, also described as without a "solid core".

Often these 5 aspects give us the impression that we are them, and they are us. But try meditating on the question: 

How can it be "you" or "yours" if you can't really grasp it? 

In the beginning you may feel that you are grasping (one or all of) these aspects, and there may be a sense of attachment to one or all of them, but gradually you will perceive that it's futile because they are changing and not completely under your control.