“Many of us crucify ourselves between two thieves - regret for the past and fear of the future.”- I don't remember who said this, but it seems to be very true.
We often regret what we have done or left undone in the past. We also feel apprehension about what the future holds. These two emotions frequently make us forget the present. But since it is only the present that we have the power to influence, it is the present that is most important.
This same thought is expressed in the following Subhaashit-
गते शोको न कर्तव्यो भविष्यं नैव चिन्तयेत् l
वर्तमानेन कालेन वर्तयन्ति विचक्षणाः ll
(We) should not grieve (शोको न कर्तव्यो) over the past (गते). (We) should not think (worry) (नैव चिन्तयेत्) about the future (भविष्यं).
Those who are learned (विचक्षणाः), act (वर्तयन्ति) keeping (only) the present time in mind (वर्तमानेन कालेन).
This is, of course, easier said than done. Most of us spend much time thinking about what 'could have been'. What we could have done differently. But no one has the power to change the past. We should learn from the mistakes we have made, but not dwell on them. Likewise, it does not help to worry about the future.
We can only influence our present time, so we should not waste our present, but live every moment.