A great astronomer was, once in his early days, working hard at
mathematics, and the difficulties he met with, made him ready to give
up the study in despair. After listlessly looking out of the window,
he turned over the leaves of his book, when the lining at the back
attracted his attention. Looking at it closely, he found it was part
of a letter written to a young man, apparently, like himself,
disheartened with his difficulties. "Go on, sir, go on," was the
counsel; "the difficulties you meet will disappear as you advance."
This short sentence seemed to give the student fresh courage.
Following out these simple words he applied himself with renewed
energy to his studies, and ultimately became one of the most learned
men of his day.