In a study published by the Journal of Personality and Social Psychology in 2004 it was concluded that:

Forgiveness, though widely admired as a virtue, sometimes brings costs for self-interest. In the wake of deep hurt, those who forgive must humbly set aside hateful thoughts and vengeful
fantasies that seem perfectly justified. To forgive means to cancel a debt, a debt for which one may fully deserve repayment. This debt metaphor suggests a profile of a person who should be especially prone to unforgiveness. An unforgiving person should be someone who is easily offended, highly invested in collecting on debts owed to the self, and determined to assert his or her rights in a principled effort to maintain self-respect. As suggested in the six studies presented here, individuals high in narcissistic entitlement fit this unforgiving profile in ways not fully captured by situational factors (e.g., offense severity, apology, and relationship closeness) or broad-based individual-difference constructs (e.g.,agreeableness, neuroticism, religiosity, social desirability). These findings suggest that narcissistic entitlement is a robust, conceptually meaningful predictor of unforgiveness.

Exline, Julie Juola, Roy F. Baumeister, Brad J. Bushman, W. Keith Campbell, and Eli J. Finkel. “Too proud to let go: narcissistic entitlement as a barrier to forgiveness.” Journal of Personality and Social Psychology 87, no. 6 (2004): 894.

The conclusion here reminds me of certain teachings of Jesus and the book of Proverbs:

In Luke 17:7-10 Jesus gives a seemingly out of place saying:

“Now, who among you, having a servant plowing or tending lambs, who comes in from the field will say to him, “Go rest, now!” Will he not rather say, ‘Prepare something to eat and get dressed to serve me until I eat and drink, and after these you will eat and drink?’ He will not thank the servant for doing what he was told, will he?” So also you, when you have done everything which has been commanded to you, you should say, “We are unworthy servants, we have only done what we must do.””

This seems to mean that we Christians should take our good deeds with a grain of salt. In other words, though God does want to bless us (which Jesus teaches elsewhere) it does not behoove the Christian to have high expectations about the nature of his or her own deeds. In the timeline of eternity they may or may not mean much, so hope in God to give them significance (which he promises to do). And then, as Paul says, “Your work in the Lord will not be in vain.” But an entitled attitude will probably cause significant anger when trials come either from like circumstances or others who mistreat you despite your hard work. Do note that this is a Proverb and not a universal principle. Jesus gives instructions about dealing with abusive authority and speaking truth to power elsewhere. So this is to be applied to those of use facing disappointment, not blanketly applied all who face injustice from legitimately un-thankful superiors.

Also, Proverbs 12:11 (ISV):

Whoever tills his soil will have a lot to eat, but anyone who pursues fantasies lacks sense.

If you pursue the fantasy of being owed something or the fantasy that crops grow without work, then you’ll find yourself going without. But it won’t only be that, but it will apparently be with a chip on your shoulder and an unforgiving heart.