Instead of living in the moment, we live for the most part in our minds, cluttered with thoughts. These thoughts are in fact part of our memories from the past. These memories are either pleasant or unpleasant, depending upon whether we had a like or dislike towards them when they occured.

For example, instead of enjoying the holiday you have been looking forward to, you spend most of your time thinking about your work whilst on holiday. You cannot fully relax and appreciate the environment around you because your mind keeps jumping back to work which you have escaped from, as you have a dislike towards it. Or it goes back to remembering your close friends for whom you have a fondness.
It is these memories that prevent us from living in the present happily. As a rule, the greater the like or dislike towards something or someone, the more consumed you will be by the memory of it and hence live in the past or rather what has been.

These memories cannot be altered and there is nothing to gain by living with them. What has happened is a past and the future is not in our control. The only thing we can do is to live in the moment, the present, and enjoy all that is in front of us.
“A knowledge that can bring settlement to the mind in every way is the complete knowledge; and that is the knowledge that can bring complete settlement” - Param Pujya Dada Bhagwan

Therefore, the only solution is to attain Self-realisation, after which you will start living in the present and not let the past affect your present. You will see each thought but not become one with it or be affected by it. You will learn to remain untouched. By remaining in the awareness of the Self, you will slowly forget to have like and dislike for the thoughts that occur from the past and start enjoying the present and living in the moment.

As one begins to learn how to live in the present, one naturally stops living in the past. It is like if you are travelling somewhere, the only way you will reach your destination is to leave your current location. Hence, as the understanding of living in the present develops one starts to experience a tension-free and a worry-free life, and begins to enjoy the present.

If you however try to stop overthinking about the past without Self-realisation, you may only succeed in making it worse or get tired of trying to do so without much success. Only when each thought is seen and known from the perspective of the Self, it dissipates forever, leaving you feeling lighter and happier.

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Author's Bio: 

Ambalal M. Patel was a civil contractor by profession. In June 1958, spontaneous Self-Realization occurred within Ambalal M. Patel. From this point on, Ambalal became a Gnani Purush, and the Lord that manifest within him became known as Dada Bhagwan. A Gnani Purush is One who has realized the Self and is able help others do the same. Param Pujya Dada Bhagwan used to go from town to town and country-to-country to give satsang (spiritual discourse) and impart the knowledge of the Self, as well as knowledge of harmonious worldly interactions to everyone who came to meet him. This spiritual science, known as Akram Vignan, is the step-less path to Self-realization.