"Therefore do not be anxious about tomorrow, for tomorrow will be anxious for itself. Sufficient for the day is its own trouble. (Mathew 6:34 ESV)

One of the main reasons why people feel down is looking back or looking ahead. Dwelling on the past leads to vain regrets because we cannot change the past. All of us have some degree of regret over decisions made in the past. Being humans, we make wrong decisions and offend other people. There are things I did years ago that make me cringe even today. The ability to move on after failures is an important skill. Of course, we need to make peace with people (usually friends and relatives) we have offended as much as possible. This will help us move away from the past sooner.

Conversely, trying to divine the future leads to fear of the uncertain and endless worry. Some people carry the weight of the future today. Our shoulders are broad enough only for today’s concerns. In fact based on research, a great majority of our worries do not come to pass (eg incurable disease, loss of job). So we suffer from things which will not happen anyway. Only God knows the future. It is futile for us to even try to know it. “The mind that is anxious about the future is miserable” according to Seneca.