I picture my todo list as heirarchical. Like, "grow my business" might be a top level entry... but beneath that, I've got, say, "improve provisioning automation," "Improve marketing," "setup backups," "create new services," then, say, under "improve provisioning automation" then we start seeing, you know, actual programs I could work on.
But, my point is, "One thing" if you don't specify how far up or down that hierarchical list, really can mean a billion things. I mean, even once I have the hierarchical list up, many tasks help with more than one higher level task. I mean, backups, for my own stuff, could improve marketing, but the way I'm implementing backups, I can sell space to people that aren't my current customers, so it's also a new service.