Why is it so hard to forgive?

Tomorrow is a holiday that many of us celebrate. We are getting ready to go celebrate Jesus conquering death to give us life.  On Good Friday Jesus was crucified, but right before he died on the cross, the thief ask Jesus to remember him. Some people would say the thief asked Jesus for forgiveness.  
With that being said, how do we expect for God to forgive us, but we can’t forgive others.  We come up with a million excuses to why we can’t forgive. We say stuff like “ I will forgive, but I won’t forget”.  What is it to really forgive?  Why celebrate the resurrection if you have not forgiven the man to your left and right?  Don’t say we all fall short of the glory of God. Look at this world 🗺. Tomorrow is not promised to us. People are leaving this world within the blink of an eye. Don’t wait until it’s to late.  

Be at peace with yourself. Know that you did what was right. You did what you were supposed to do. Know the reason why you really celebrate the resurrection.