Most of us strive to to avoid pain and try make the world meet our expectations. One way of creating what we want is envisioning a mental image and asking for it to be given. And when it is, we can choose to be grateful for the shape it comes in or we can insist that we know better and it should have been more exact to our specifications.... and by doing so, make ourselves dissatisfied. Refusal to accept something is the result of the conflict between the reality of how something is and the way you want it to be. The world does what it does regardless of whether it has your approval, so your choice is to resist and create pain, or accept and find a positive perspective that allows you to feel good about it.
Other people, even those people we deeply love, just don't "act right" sometimes. They make decisions that we don't like and do things that are not in accord with our values and desires. So we can resist and argue and be angry and resentful, or we can accept them as they are and choose to love them anyway. Our refusal to accept other people, places or things the way they are creates negative emotion. Our ego likes to argue with reality, to insist on our desires and perceptions as being right, frequently leaving us facing the choice of being right or being happy.
What is, is. It is our thinking about it that creates the pain or pleasure, and perhaps it is our thinking that created what is in the first place. So I like to ask "What is it about me that is drawing this experience to me at this particular time? What I am doing to create this and what can I learn from it?" If everything is part of earth school, and we create our own reality, then on some level I chose this experience. And then I can choose the perspective that whatever it is, it is in my best interest because everything unfolds in perfect divine order. And when the reality is a loss, a death, large or small, I grieve it and I give thanks for what I once had and practice the fine art of letting go with love. And I recognize that it is called practice because it is something I do over and over with the intention of getting better at it.
Acceptance does not mean that we necessarily like or approve of what is, but simply that we acknowledge it as being that way and choose to be OK with reality. In order to get to where we want to go, we have to start where we are. Remember that our reality is determined by our perceptions, by our thoughts. We can recognize the existence of something without having to like it and still find a way to practice gratitude for it. Which reminds me of the story Father Martin used to tell about two boys: One boy was left in a room filled with toys and games and candy and pretty near everything a boy his age could want. A second boy was left in a room that was wall to wall manure. An hour later, the first boy had not touched any of the goodies and when asked why, said that he knew he would have broken the games and gotten sick from eating too much candy, so why bother. In the other room, the second boy was happily shoveling the manure and whistling. When asked what he could possible be so cheerful about, the boy smiled and replied, "Mister, with all this crap in here, there's gotta be a pony somewhere."
"When you are praising, when you are appreciating, when you are acknowledging value, when you are looking for positive aspects, when you are laughing, when you are applauding, when you are joyous, when you are feeling that feeling of appreciation pulsing through you, in those times there is no resistance within you. You are in those moments, vibrationally up to speed with who you really are." Abraham / Hicks