Sentence:  If you like being in there at the beginning of a company then get ready to bail out when the company starts to grow. Never <WSD>let the grass grow under your feet</WSD>. Jobs for life are history, so if you treat people right but they still want to move onto new things you can't stop them. 
Meaning of the word marked with <WSD> tags:  To settle in one place rather than moving to another.