Saying sorry when you have blundered , changes the energy of a situation . It clears the air , when you have done something wrong to others , they have anger, resentment and a whole plethora of feelings. You press their buttons if you like.
They then think unkindly of you.
So here starts a karmic situation.
To clear it is to take responsibility for your actions, say sorry . It takes courage and honesty from you to admit you are in the wrong. It is not a sign of weakness.
Unresolved issues between people can fester over the years and become a huge energetic block,thought form which hangs around you like a weighty cloud. Act straight away , say sorry. This tops build up of unwanted skeletons in the cupboard.