The statement asserts that it is the later generations but not those ones who live in the same times that decide the greatness of great figures. I strongly agree with the statement. The greatness of individuals comes from their achievement to the development of the society, and no one in the same contemporary can predict the influence imposed on the long-term development of society is beneficial or harmful, in a word; greatness should be tested over time before it can be confirmed.
In the history of science, many of the great figures that we show our wholehearted respect to nowadays didn't get the honors deserved from their contemporaries or even died in obscurity. These figures could not be admitted at that time mostly owned to the limitation of nudge of the times and the perspectives that people see the problems. A compelling example is from the Polish astronomer Gopernicus, who invented the sun-center theory, which is opposed to the earth-center theory prevailing at that time, the theory was considered ridiculous and Copernicus was ridiculed even quelled by the region and the comtemporaries. As time went by, the theory was demonstrated to be correct and reevaluated after his death, it us, the people who live after him give him the justifiable comments.
When it comes to the realm of politics, the greatness mostly lies in its enduring influence to later generation. Take Hitler, the biggest sinner of the world for example. He made a lot of strategies, which did help, develop Germany economic rapidly and became one of the powerful nations in the world, and gained much respect from his people which help develop his scheme of becoming the number one bash of the world by armed aggression to other coutries, the so-called the second world war. It is vivid to us that he was regarded as a great man by his comtemporaries before the Second World War, and later his ambitions gradually showed up, the grave disasters brought by him destroyed the entire good impression in people’s mind. Therefore, the greatness of figures cannot be decided by contemporaries and only the later generations can clearly identify his real essence objectively.
In sum, because the limitation to knowledge background and the satisfaction with superficial acquaintance held by the comtemporaries, the influence of some figures on the long-term social progress can not be predicted and admited by temporaries so it is impossible for them to justify any greatness of people, but the people live after them. Only in this way, great people would receive the relatively justifiable evaluation.