It is easy for someone to say, stay in the present moment, but doing it is so much harder. Actually it's quite easy to do; what's difficult is to stay there for any length of time for it to be beneficial. If you are seeking the present to attain peace because your past is too painful, or you don't like your current situation, or perhaps you're not looking forward to something in your future, then it's going to be almost impossible to stay in a state of peace in the present moment.
To be at peace in the moment, you have to be at peace with what has happened to you. You also have to be looking forward to who you are becoming and then 'know' that right now your are in the perfect place.
The reason it is so important to be at peace with the past is that it is simply a collection of our life so far. If we focus on some of the traumatic moments or the times when things were not working so well, then it will reactivate these memories and bring an element of this pain into the present. If many things from day to day life trigger off these memories they will set of an element of pain often happening outside our awareness.
Let's say something horrific happened, very traumatic yet we survived. It would only be natural to 'see yourself' as a survivor. That is, your sense of self is now based on being a survivor. The way you see yourself alters the way you will interact and perceive reality, and, as a consequence, alters your quality of life.
If I am a survivor my whole reality is based upon what happened (the traumatic thing). My day to day actions are then all in some way related to this painful event.
If someone was to see, for example, the painful event as a wound that created a sensitivity, which altered their character in such away that they became more compassionate and caring towards others, and, as a result, with this new sensitivity they helped others to heal and grow, then they would not see themselves as a survivor; but as an alchemist (turning lead into gold).
If you only knew how so many great people managed to turn their challenges and struggles, their stresses and traumas (coal) into wisdom, kind deeds, motivation and power (diamonds) then you too could do the same.
First thing is to be aware that you can turn your past traumas into gifts.
Secondly you have to see what the gift is.
Then you have to know how you can give this gift,
Then give it - constantly.
When you can see your past in a way that provides you with possibilties for growth then you will be richly rewarded with opportunities for growth. However if you see your past as the source of your limitation, then it will keep you stuck in a pattern, that provides no opportunity for growth.