I'll tell you what makes me cranky pretty much every day. The caregiving never ends. Never is there a point where I do something in caring for Skip and I say to myself, "well, that's done then."
And the demands have increased over time and will increase as the years go by. Unlike kids, who grow up and become independent (yeah, yeah I know they're always your kids, but the active care for them day in day out ends in the vast majority of cases).
It's important for me to get breaks from the demands of caregiving. Without them, my ability to approach caregiving in good humor diminishes to almost nothing.