Dua is nothing but a wish which gives some mental peace to self but also weaken our abilities or self reliance when we leave result on God and sleep.
A bridge won't sustain if not done as per specs whatever duas done. A student won't pass without hard work whatever duas are done by parents. A patient won't survive with duas. City water will finish without dams, no dua will work.
Isaac Neuton's ,(1643-1727) third law is divine, every action has a reaction.