Forest Dhamma: A Selection of Talks on Buddhist Practice is written by Acariya Maha Boowa and translated by Acariya Panyavaddho. All of the Buddhas declared that training the heart to achieve happiness is the right and genuine path. Our hearts aren't fundamentally different from those of animals when they never get a chance to rest and settle down.
However, we will be able to notice the negative effects of thinking and fantasizing, as well as the turbulence they generate in the heart, when our hearts rest, relax and receive training. Then we'll realize how important it is to have a tranquil heart. We will have reached the first level of Dhamma when we have reached a state of mental tranquility that will guide us steadily forward.