I think it's less that we forget, more that we choose not to remember.
Most harm done us is carried out in ignorance, i.e. the perpetrator either does not realise the damage caused or is too thick to understand or care.
Those people need our understanding, we may not like it, but we are required to forgive if we expect to be forgiven.
Once you accept that people can be morons and cause you grief, it becomes possible to choose not to remember their actions.
So no we are not equipped to forget things totally, there will always be something that may trigger the memory, but allowing that memory to cause bitterness will only harm us.