A lack of caring is one of the main signs of depression. Depression isn’t so much the sads but a lack of caring/motivation regarding life. That’s why you see depressed people often have sinks of dishes or piles of laundry. It starts with one “fuck it” and gets worse from there. Of course as the pile gets larger then it takes even more motivation to clean and in the meantime every time it grows you’re frustrated with yourself and mentally beat yourself up. You beat yourself up enough it makes you not care about your life, you stop caring if drivers see you when you cross the street, you daydream about being in an accident on the way to work/shool. Etc until you get help/better or suicide (likely fail) and then get help/better.

This is different from not caring about the little annoyances in life.