"No matter how hard the past, you can always begin again." 
-Gautama Buddha

"When the human organism is discharging its negative experience efficiently, the mind is empty of past or future concerns; there is no worry, anticipation, or regret. This means that the mind is left open to Being, the simplest state of awareness."
-Deepak Chopra

"If you have a friend who suffers, you have to help him. 'My dear friend, you are on safe ground. Everything is okay now. Why do you continue to suffer? Don't go back to the past. It's only a ghost; it's unreal.' And whenever we recognize that these are only movies and pictures, not reality, we are free. That is the practice of mindfulness." 

-Thich Nhat Hanh

"When you surrender to what is and so become fully present, the past ceases to have any power. You do not need it anymore. Presence is the key. Now is the key." 

-Eckhart Tolle

“We are not held back by the love we didn’t receive in the past, but by the love we’re not extending in the present.” 
-Marianne Williamson

"In truth, to see anything without love is to see it fearfully. Threat doesn't arise "out there." Its origins are "in here," where we first establish our beliefs. Every threat is a shadow from the past." 

-Deepak Chopra

"The secret of health for both mind and body is not to mourn for the past, not to worry about the future, not to anticipate the future, but to live the present moment wisely and earnestly."

-Buddha