There is an old saying, "Hard work is never wasted effort." However, your hard work can become wasted effort by just one careless word from your lips. If you complain when others don't recognize your service or faithfulness, or if others are hurt because of your words and peace is broken, then even though you worked with all the goodness of your heart and worked very hard, it is like trashing your rewards with your words.
"For we all stumble in many ways if anyone does not stumble in what he says, he is a perfect man, able to bridle the whole body as well" (James 3:2).