All spiritual texts and teachers stress on living in the present. That is concentrating the mind on what is going on now at this moment.
We ordinary people mostly live either in the past or future.
We live in the past by voluntarily or involuntarily stirring our memories and getting subsequent related thoughts and feelings.
A human being is essentially a mental being. As long as he is awake his mind incessantly works getting thoughts and feelings related to past or future and very rarely from ongoing happenings.
Worry, pain, ache, remorse, like things are experienced through the thoughts about past, which is present in us in the form of memories.
The mind when focusses on future, fear, anxiety, tension, imaginations, doubt are felt through thoughts and feelings.
Thus past and future are nothing but related thought-forms in the present not allowing us to concentrate on the present happenings.
As a man is essentially a mental being, he gets drawn by the whirlpool of thoughts relating to past or future.
This makes one unhappy and disturbed. The lack of mental strength to come out of this whirlpool of thoughts is common to us all.
In reality neither past nor future physically exist. They only exist in our mind as thoughts and feelings.
We are aware or not, three conscious states of mind arise and disappear in us. They are state or phase of wakefulness, dream or deep sleep.
Deep sleep is when our mind in the form of thoughts and feelings takes rest. We don't get thoughts or feelings and our awareness of us - the self-consciousness too will be absent.
We function mentally during wakefulness and dream conscious states of mind assisted by deep sleep phase during or in between.
Having strength of mind not to go to past or future as thought forms saves us of lot of mental energy being wasted.
J Krishnamurty has almost completely rid of his memories after the under the pine tree experience in the USA. Thus he is saved of thoughts from the memory. Many seers though are aware of past don't allow it to poke its nose now.
They consciously don't indulge in thoughts about future. Thus they save themselves from the inconvenience caused by the "future".
To cultivate mind to live in the present, human beings can take the help of spirituality.
Not getting thoughts or feelings