Sentence:  His sense of humour, together with his rationalism and ideology, helped me enormously on my road to recovery. Bruce eventually convinced me of the need to move on. “Que sera sera,” he would often say to me. “Ya can't <WSD>let the grass grow under yer feet</WSD>, me old mate.” 
Meaning of the word marked with <WSD> tags:  To settle in one place rather than moving to another.