Unfortunately, we are not all perfect, and some people have not been well catechized, do not understand the importance of what is going on at the Mass, or allow worldly concerns to enter into this sacred space and time (thus the temptation to carry on unnecessary conversations, etc.).
Sometimes people have a legitimate reason to say something to a neighbor or leave early, so perhaps we shouldn’t judge any individual too harshly without knowing the details (although I admit this happens too often, and not always for good reasons).
I tell myself it is not my concern but it distracts me from fully participating in the mass and staying focused. How do I overcome this obstacle?
I too have had times when I had a hard time focusing on the Mass because I was focusing on others’ behavior. But then I realized that I was reacting just the way Satan would want me to — anything that distracts from the Mass pleases Satan, and I was playing into his hand.
When it happens, just try to bring yourself gently back to prayer: say a brief prayer for the offending person and then return to the Mass; or ask the Blessed Virgin Mary to accompany you as you pray the Mass (after all, she was at the foot of the Cross, and that is where we are when we are at Mass); or ask your guardian angel to remove the distractions until after Mass when you can address them if you need to.
God bless you, and welcome to the Catholic Church — a wonderful place to be even though it is full of imperfect sinners like me!