While throughout history there have been people who realised the Earth was finite, too few have stopped to fully contemplate grok the concept. Grok that the area of the Earth is finite, that the resources of the Earth are finite, and the time the Earth will exist is finite. It was not until the 1700s that a significant number of people in different countries could even accurately picture the planet entire planet and appreciate the surface was finite, and not until the 1900s that the term 'sustainability' attracted significant attention, and people started to appreciate how resources are finite. This missing piece in this picture is still time, with most people still having a time horizon that allows time for our planet can be considered infinite, even though finite, and there is less than 2% of time remaining for life on Earth.
One, because given it took 4 billion years before life could exist on the surface of this planet, it is going to take a long time to ever find another. Finite, because no matter how obvious it is the planet is finite, it is large enough for us to mistakenly overlook that the planet being finite impacts everything from the environment to the economy.