"That's just the way I am." When we hear this, someone's usually telling us to "Get off my back" or "Accept me as I am."
Often it's a response to us criticizing them. It could be about the person's chronic lateness, thoughtlessness, broken promises, physical or verbal abuse, or infidelity. Whatever it is, we're asked to let it go.
In the end, this is a ploy to get us to lower our expectations, based on the dubious idea that bad habits are an intrinsic part of character, and therefore beyond our control. We're expected to believe it's foolish and futile to expect others to change.
Lots of things, of course, are beyond our control: short stature, big bones, receding hairline. Fortunately, character is different. That's completely within our control. The poor and the rich, the slow and the smart, the plain and the pretty all have an equal opportunity to become people of character.
Sure, character can be influenced by heredity and environment, but it's determined by choice. No disposition, circumstance, or experience is so powerful that it forever fixes our character. Our character is never finished. It's constantly shaped and sculpted by the choices we make to nurture or ignore our more noble instincts and to surrender to, or overcome, negative impulses and corrupting temptations.
When it comes to what we demand of ourselves or others, we should never lower our standards. Character is a function of choice. Weaknesses and bad habits are not excuses not to get better.