An immediate reaction to the spiritual practice of acceptance is to think of examples where people really shouldn’t accept their reality.
People in abusive relationships, victims of crime and mistreatment, exploitation, unhealthy situations generally.
We think of these examples because “acceptance” is often understood in a non-spiritual context to mean simply putting up with something, not resisting, not changing.
In this mundane sense we can say that great leaders of social change like Gandhi or Martin Luther King were significant precisely because they did not accept the status quo, did not accept the received wisdom, and instead fought for change.
But in a spiritual context acceptance was the secret behind the success of the Indian independence movement and the civil rights movement. Gandhi in particular excelled because he first accepted the reality of British rule and the legitimacy of the British governance of India. He accepted that there was some truth to the British claim that India could not govern itself, that it lacked the political organisation, seriousness, and moral responsibility for self-governance. That is why he eschewed violent means of protest, because he wished to make the moral character of the Indian people an irrefutable reality.
This conflict between the mundane and spiritual aspects of acceptance arises because human beings are autonomous and reflective. We can choose how to act, and we can reflect on our actions, reactions, and intentions in a self-aware way.
This is important because when we come to accept reality, we need to realise that our reality includes not only the things in our environment, but also our reaction to that environment.
If I get angry at my home always being messy, the mundane form of acceptance would be to try to feel okay about my home being messy, to stop getting angry at this undesirable state of affairs. This is a mistake, because it ignores or rejects the reality of my pre-existing emotional, mental, and physiological response.
The spiritual form of acceptance begins with accepting both the messiness of my home, and my anger at this state of affairs. It means accepting the whole package, the whole experience, the whole reality.
If I do not accept my anger, then I am merely fighting with myself in denial of reality.