Given notion is although correct in some situations, but it is not the case which is always true. We can estimate greatness of personalities, only when we are able correctly construe their deeds. This understanding process, sometime takes years; therefore, there are some cases, where greatness of some people is praised posthumously.
Galileo, the famous philosopher, disabused some commonly followed conventions of catholic church. People of his times were not able to recognize his ideas, because they found them impossible according to their believes at that times. After some centuries, when scientists expressed consensus with Galileo’s idea, Galileo’s greatness was confirmed by the world. We can see that this case reasonably supports the given notion.
However, if contemporary people are knowledgeable enough to admire, to understand the greatness of someone, the case is completely different. For example, when Archimedes formulated the buoyancy principle, his king reward him for his success. King was cognizant of what actually he (Archimedes) had done; this made him to recognize the greatness of this early scientist.
Now days, we have enough facilities like patents, publications , conferences, manifestos etc.; this makes anyone of us to easily present his or her ideas. Therefore, with these facilities new generation is less likely to conform the given notion. For example, we can evaluate a politician on basis of her work records and manifestos. Similarly, a sports person can be judged on grounds of her performance in concerned sports; her games could be easily viewed on television, and we can then decide her greatness on basis of her game play.
Thus, we can see that given notion is rarely having any significance in present world. Though, this notion was true in some earlier times, when there was a severe deficit of intellectual skills, like for example, at times of Galileo. But now time has drastically changed; now people are having enough knowledge to assess; to wisely decide ones worthiness; to determine the virtue of one’s greatness.