The Act of Contrition is part of the Sacrament of Penance and is prayed by the penitent after the priest assigns a penance and before he gives the penitent absolution. Penance is repentance of sins.
Repentance is a stage in Christian salvation where the believer turns away from sin.
Here's the prayer:
"O, my God, I am heartily sorry for having offended Thee, and I detest all my sins because of Thy just punishments, but most of all because they offend Thee, my God, Who art all good and deserving of all my love. I firmly resolve, with the help of Thy grace, to sin no more and to avoid the near occasions of sins."
The act of contrition prayer is also customarily said especially before one goes to bed at night.
The prayer reminds me that I am not perfect. It is also shows us the way to forgiveness.
The Catholic definition of contrition is showing sorrow for your sins.
I remember John Donne quotes "Death comes equally to us all, and makes us all equal when it comes. "
Some people says that "the act of contrition must be done everyday. It's a confession to God, because you will never know when your last day on earth is."
Life is short. Time is fast. No replay, no rewind. Enjoy every moment as it comes.