Goldilocks conditions refers to the Earth seemingly at the perfect distance from the Sun, in order to sustain oceans of liquid water for life; just as Goldilocks, in the story of Three Bears, found the porridge that was just right.
Venus is too close to the Sun, and too hot for flowing water on its surface. Like a sauna, the ancient waters of Venus had evaporated into what is now a very thick and heavy atmosphere.
Mars is too far from the Sun, and too cold for liquid water to be maintained on its surface. Mars also does not have a continental drift, so particles of the atmosphere which become trapped within the ground, stay trapped within the ground. Thus over time, the atmosphere of Mars has become thin, while all the water is frozen into the ground.
The temperature of Earth is just right for flowing water on the surface, and for rock that allows for continental drift. With continental drift, particles of the atmosphere which become trapped within the ground, are brought back to the atmosphere through eruptions of volcanoes. These conditions cause refreshment to the planet's atmosphere. A medium sized atmosphere helps keep temperatures just right for flowing water with a stable greenhouse effect. These conditions are just right for abundant life.