The first is tell others to get off their chairs and do some work. (Idiomatic condemnation).
Don't let the grass grow under your feet! - Don't sit there like a sack of potatoes, or let circumstances overtake you by your inactivity.
On the flip side. (Idiomatic affirmation).
I don't let grass grow under my feet. - I'm constantly active and looking for solutions. I'm restless and as a result the ground under my feet is always being trampled to the point that any weeds or unwanted plants are unable to take root. I like to imagine flames down there. In summary:
a hard working person who adapts, changes and moves on "does not let the grass grow under his or her feet".