If you spend any time around a farm or a garden center, it is easy to see how true this statement is. If you are looking at a healthy, vibrant peach tree, you will eventually see plump delicious peaches coming off that tree. If on the other hand, you are looking at a tree that is withered, with no flowers, and infested with a disease, you know you will not see good fruit being produced. The same goes for humans, if a person is bitter, angry, giving off what is called a toxic atmosphere, it is pretty easy to tell that on the whole they are not living a productive life. You can witness that on social media every day. People post angry, nasty remarks about others, and often they do not even know the people the are posting about. They just have a need to spew hate or sarcasm.
On the other hand, you can see people who are joyful, smiling, and generally looking at life through the lens of a person who is happy to be alive. These people often reach out to others to offer help, they run animal rescues, they do not condemn others, they talk to others. After meeting them and spending time with them you come out of it feeling better about yourself. If you want to insure you live a productive life, trying starting out the day reading something from the book of \Proverbs, read the Gospels, just give a quick thanks to God for giving you another day on this earth to celebrate your productive life.