"On Duties" is widely considered Cicero's best work. This beautiful piece of art contains a plethora of wisdom, mainly focusing on the question "Is the right thing to do always the advantageous option?". This simply means that if you always do right, you will find that it is the most advantageous path. Let's take a look at a quick example.
Say you are selling bottled water and a server drought hits the local community. Water is very scarce but you have an almost unlimited supply. The perceived options would be to sell the product at the normal price (or cheaper) while the second option would be to increase the cost of your bottles of water and make a nice profit. The first option would be the right thing to do and the second would be the more advantageous. Cicero argues that the second options would actually be worse for business. You may make a nice profit at first, but once the drought is over you will likely never sell a bottle of water again. At least not to any of those people.
Historically this work ends tragically. Cicero wrote this for his son and concluded that he hopes to see him soon and that this story should be taken as the best gift he could possibly give. The truth came to be that Cicero never saw his son again. Shortly after writing On Duties, Cicero was killed by order of Mark Antony. Cicero's son, many years later, would get the distinct honor of announcing Antony's defeat by Octavius at the Battle of Actium. A final act of revenge.
On Duties will keep you deep in thought, and in the end, this is why we choose to read this type of work. I rate "On Duties" 4.2 / 5