By definition, a simile is a figure of speech that describes one thing by comparing it to something else that is quite different. Also, the comparison is made through the use of "like" or "as". One thing is "like" or "as" the other. Sometimes a writer creates a simile and then develops it with details. A developed simile is called an "analogy," and Ben Franklin included several of them in his autobiography.
When Ben was working on perfecting his own character, he decided to concentrate on one virtue at a time; when he failed, he put a black spot in his little book. He compared his removing the black spots (his failures in being virtuous) to a gardener's pulling weeds:
And like him who, having a garden to weed does not attempt to eradicate all the bad herbs at once, which would exceed his reach and his strength, but works on one of the beds at a time . . . so I should have, I hoped, the encouraging pleasure of seeing on my pages the progress I made in virtue, by clearing successively my lines of their spots . . . .
This basic simile is structured with "like" in its beginning. Ben says he is "like" the man weeding his garden in how he goes about perfecting his character.
Another simile that is developed into an analogy is found at the end of his autobiography when Ben uses "as" to compare his efforts to perfect his character to the efforts of those who try to perfect their handwriting:
. . . though I never arrived at the perfection I had been so ambitious of obtaining, but fell far short of it, yet I was, by the endeavor, a better and a happier man than I otherwise should have been if I had not attempted it; as those who aim at perfect writing by imitating the engraved copies, though they never reach the wished-for excellence, their hand is mended by the endeavor . . . .
In this extended simile, Ben says he is "as" those who fail to write perfectly. They never write perfectly, but their handwriting is much improved. Ben never reached perfection in his character, but he becomes a better man for having tried.