I agree that rationality and reasonableness can be similar, but they can also be different. See this post for what I mean by rationality. The idea of it being choosing the best option is too vague.

Some factors that may lead to what others think is reasonable being different from what is the most rational are: the continued use of old paradigms that are known to be faulty, pushing your views as being what is reasonable as a method of control and status quo bias.

Here is are two more examples of the predicament

• Imagine that you are in family that is heavily religious and you decide that you are an atheist. If you tell anyone in your family you are likely to get chastised for this making it an example of the just-be-reasonable predicament.
• Imagine that you are a jury member and you are the cause of a hung jury. They tell you: “the guy obviously did it. He is a bad man anyway. How much evidence do you need? Just be reasonable about this so that we can go home”. Now, you may actually be being irrationally under confident or perhaps you are not. The post was about what you should do in this situation. I consider it a predicament because people find it hard to do what they think is the right thing when they are uncertain and when it will cause them social disapproval.

Also, I have updated the below:

The just-be-reasonable predicament occurs when in order to be seen as being reasonable you must do something irrational or non-optimal.

To this to try and more clearly express what I meant:

The just-be-reasonable predicament occurs when you are chastised for doing something that you believe to be more rational and/or optimal than the norm or what is expected or desired. The chastiser has either: not considered, cannot fathom or does not care that what you are doing or want to do might be more rational and/or optimal than what is the default course of action. The predicament is similar to the one described in lonely dissent in that you must choose between making what you to believe to be the most rational and/or optimal course of action and the one that will be meet with the least amount of social disapproval.