Bacon's Essays, written in three groups between 1597 and 1625, are Bacon's attempts to guide men to appropriate actions in their personal, business, and public lives--they are, in essence, the 17thC version of "How to Succeed."  Bacon's essays are filled with practical advice on every important aspect of a man's life, but they are focused on practical, as opposed to morally ideal, success in the world.  In his essay "Of Simulation and Dissimulation," Bacon defines the terms and then advises the reader on their use and the dangers in their use.

Bacon argues that both simulation and dissimulation are useful but their successful use requires both intelligence and "a strong heart," that is, confidence.  Dissimulation Bacon defines as "when a man lets fall signs and arguments, that he is not, that he is."  In other words, dissimulation allows others to misunderstand what he is doing and thinking--he fails to correct misconceptions about his behavior.  Simulation, on the other hand, is much more active: a man takes actions that disguise what he is really thinking and doing.  Dissimulation and simulation are two of three levels of a man's method of hiding or veiling his motives, the first of which is "closeness, reservation, and secrecy," that is, a man hides himself sufficiently so that no can easily observe his behavior.  We might call that today shyness, modesty, reserved behavior.  Bacon argues that secrecy is "both public and moral" because being "open," telling everyone what one thinks about everything, leads to people concluding that the person cannot keep confidences and is therefore weak.

Dissimulation, according to Bacon is

a necessity; so that he that will be secret, must be a dissembler in some degree. . . .So that no man can be secret, except he give himself a little scope of dissimulation; which is, as it were, but the skirts, or train of secrecy.

The implication of Bacon's argument is that, for a man to get along in this world, he has to be able to maintain a certain degree of secrecy at times, and that secrecy is, in part, a product of dissimulation--allowing people to conclude one is acting one way but, in reality, acting in a different way.

Bacon's view of simulation, however, is less positive:

. . . simulation . . . is a vice, rising either of a natural falseness or fearfulness, or of a mind that hath some main faults, which because a man must needs disguise. . . .

Because simulation requires active falsehood--that is, taking actions and saying things that disguise what one is really thinking and doing--it is  a sign of a deceptive nature and is not just a way of creating secrecy so that one can act freely.  The essential difference between the two is that dissimulation is a passive way of letting people think what they may about a person's actions, but simulation requires that person to actively deceive, which, according to Bacon, is a sign of a bad character.

Both techniques, though, are useful according to Bacon: 1) they lull opposing parties into false security; 2) they help disguise a man's motives and actions; and 3)they create an atmosphere in which another man may speak freely because he does not know what the other party thinks about the subject under discussion and may assume they are of one mind.