Many take this quote from Mark Twain at face value and interpret it to mean we must be sweet and forgive those that we perceive have wrong us.
There is so much more here that needs to be digested.
First of all, to forgive another is not so much an olive branch or peace offering to assuage their feelings as it is a release of the anger and resentment we hold that is causing us pain.
Then we must broaden our scope to include all of the conditions we are exposed to in life through our contacts, travels, interactions and even the news and media. None of these situations are personal and only holding on to our vitriol surrounding them will give them power to hurt us. The shroud of our forgiveness and letting go blankets us in the sweet aroma of contentment once again.
However the most valuable point behind the idea of being forgiving is to cut ourselves a little slack. We tend to judge ourselves more harshly than our staunchest critic and grade all of our performance lower than need be, ushering in feelings of dissatisfaction and self loathing.
Know that at any given moment we do the best we can with the situation we are in and love yourself for it. Whats done is done. “Let the dead bury the dead”

No need to forgive the world while punishing ourselves.
Let it all go. Live for the moment. Smell the violets.