Why is Biblical Forgiveness So Hard?

The Passage  

Matthew 6:5-15, NASB

5 “And when you pray, you are not to be like the hypocrites; for they love to stand and pray in the synagogues and on the street corners so that they will be seen by people. Truly I say to you, they have their reward in full.

6 But as for you, when you pray, go into your inner room, close your door, and pray to your Father who is in secret; and your Father who sees what is done in secret will reward you.

7 “And when you are praying, do not use thoughtless repetition as the Gentiles do, for they think that they will be heard because of their many words. 

8 So do not be like them; for your Father knows what you need before you ask Him.

The Lord’s Prayer

9 “Pray, then, in this way: Our Father, who is in heaven, Hallowed be Your name. 

10 Your kingdom come. Your will be done, On earth as it is in heaven.

11 Give us this day our daily bread.

12 And forgive us our debts, as we also have forgiven our debtors.

13 And do not lead us into temptation, but deliver us from evil.

14 For if you forgive other people for their offenses, your heavenly Father will also forgive you. 

15 But if you do not forgive other people, then your Father will not forgive your offenses.