It means either that you are working at full capacity and cannot go faster or do more, or that you are in an untenable position and the only way out is full-speed forward.
In business, it suggests the changing of official policy or strategy or the changing of the accepted view across an industry—usually toward something unpredictable or unlikely.
To “hard sell” something is to use aggressive tactics to sell the item, including persistent marketing, verbal battering, and illicit product positioning.