"Treacherous tears" in Chinua Achebe's No Longer At Ease appears twice, both times very near one another and at the opening courtroom scene of the novel. The frame story set forth in the beginning comes around full-circle at the very end when the packed courtroom and weeping Obi are revisited. While chronologically nothing happened during the opening and closing courtroom scenes, the entire novel is a flashback focused on answering the question set forth at the beginning: why did an "educated", honest young man trained in England with so much "promise" take bribes? While Chinua Achebe fumbles with the word treacherous, his accompanying message remains largely intact: the promise of education is merely superficial as it brings more problems than it solves.
A writer's use of words must be critically analyzed to see if it has a special meaning. The phrase "treacherous tears" does not convey a meaningful message in and of itself. Adjectives of philosophical quality (such as treacherous or for that matter evil, good, or betraying) can only apply to entities capable of either understanding or acting in a way that is described by the philosophically qualitative adjective. Because a tear resulting from happiness cannot be distinguished from one in anger, the demarcation of "treacherous tears" is wrong. Just as it would be foolish to say that the bullet(s) that killed President Kennedy was/were evil, it is just as mistaken to call tears treacherous. In this sense, a dam that keeps back floodwaters and prevents thousands of people from being killed isn't good either, not because the prevention itself isn't good but because the dam itself isn't capable of understanding good. Relating this back to the novel, it would also have been a fallacy to call Obi's bribe money betraying.
In all of these three theoretical instances, the adjective (i.e.: evil) that describes the inanimate object (i.e.: bullet) that it itself is unable to comprehend the quality that describes it is simply symbolic of the individual (i.e.: Kennedy's assassin) acting on the object to make it evil, good, or betraying. For example, it's not the evil bullet that killed Kennedy, but the evil assassin who killed Kennedy. It's not the good dam that prevented the flood from destroying a town and killing its inhabitants, but the good engineers who had the foresight to prevent such a flood. It's not the bribe money that betrayed Obi but the undercover person acting on behalf of the police that tempted Obi who betrayed him. As it can be easily and logically ascertained, these scenarios merely use a convention, albeit incorrect, by placing the qualitative adjective on the object that is incapable to receive the adjective. However, we can conclude that the adjective, without loss of meaning, should simply be transferred to the person to whom it's actually referring.
A problem arises with this "inanimate to person" transfer. Obi himself does not show treachery in any sense. While he does take the bribe money that he vows never to take, it's merely out of practical necessity and survival. He needs money to live the life that is expected of government officials: buying a car, buying a nice house, supporting the family, paying back loans, and paying income tax. While on paper his income surpasses the income of anyone in his own town, the expenses that he has to pay proportionally squander all that he has. Obi doesn't want to live an overly frivolous life, just one that is expected of people his socioeconomic status. However, with the small pay (relative to the great expenses), he is forced to take bribes. Simply put, it is not Obi's fault that he takes bribes as he needs them to survive. Therefore, the part of treachery is not on Obi's shoulders, it must lie somewhere else.
The real treachery in the novel is not Obi's tears or even Obi himself. The treachery is of the promise of education mentioned in the same courtroom scene as the treacherous tears. Essentially, the colonizers' view of the native population is symbolized by the dedicated and upright Mr. Green who thinks he is superior to the native population and labels them all in derogatory terms. In short, Mr. Green thinks Nigeria's problems would be solved if it didn't have any Nigerians, quite the humorous paradox. This ideology makes it impossible for him to realize the nuances of handing over governance to Nigerians themselves. Namely that on one hand the British expect Nigerian officials to be honest and trustworthy, while on the other hand they don't pay them enough to support the very lifestyle they are supposed to shine onto society as a motivator. As the novel clearly shows, it is the rat race that is the heart of the treachery: If you are honest, you cannot live as a government official is expected, and (stated as the contrapositive) if you live as a government official is expected, you cannot be honest.