What causes a person to not forgive and hold a grudge? Is it pride?

I wouldn't call it a grudge. I call it a reminder. I think some things cannot be forgiven. I wanted closure and I will never have that. Anger is what I have too. And disappointment. I cannot understand why some people are that cruel when you have been told they love you. Or when some people do such atrocities that you cannot believe you are related to them either by blood or by being human. That's about it.

It’s usually how bad the other hurt them .

For me it was I was badly hurt .I found my ex wife in bed old enough to be her dad and it was her dads best mate .I later found out that he was also a convicted pedophile who had done time for molesting his own kids and she was still with him .

not pride, i think its more of not wanting to deal with it again. some things cut deep and dont really heal or heal properly.

Sometimes.

And sometimes it's pain and most of us having a natural impulse to seek ways of protection after being hurt, remedy too. True forgiveness takes time and accepting that we are never safe. Even those we trust the most can/will hurt us. It also requires acknowledging our own failures, without being too hard on ourselves. We treat ourselves the way our parents treat us and so we would be just as cruel or kind.

I have seen instances of people claiming to be forgiving because of their pride. "I am a forgiving person. I am better, doing better."

I'd say pride, or ignorance. It hurts the person holding the grudge the most.
Wait. Is pride ignorance?

I always thought it was stupidity! Because it's stupid to hold a grudge!

Hurt that festers and then turns into bitterness!

No it's called Hurt

Sometimes they are shallow or full of them themselves or don’t have the mindset to talk something out or forgive.

On here they just block and report like pussy’s because they don’t have the vocabulary to express what they are thinking.

It depends. Pride is one thing but most thing is betrayed, waste of time in commitment that fails

I forgive and I do not hold grudges,but it doesn't mean I will give them acess back into my life

it is the nature of the offense.

Anger.

Hurt