what does "have a little mercy" mean in the following sentence?

Question

what does have a little mercy mean in the following sentence?

To get there, you need some mechanism to fool people -- for workers to see their wage rise, but not realize that other wages and prices are also rising; for companies to see their prices rise, but not realize that wages, costs, and competitors' prices are also rising. You need some mechanism to convert a rise in all prices and wages to a false perception that everyone's relative prices and wages are rising. There are lots of these mechanisms, and that's what economic theory of the Phillips curve is all about. The point today: it is not nearly as obvious as newspaper accounts point out. And if central bankers are a bit befuddled by the utter disappearance of the Phillips curve -- no discernible relationship, or actually now a relationship of the wrong sign, between inflation and unemployment, well, have a little mercy. Inflation is hard.

https://johnhcochrane.blogspot.co.uk/2017/10/how-does-inflation-work-anyway.html#more

Answer 1

Sometimes the easiest way to get to the crux of the meaning in a phrase is to strip it down to its barest essentials. In this case, I pared this phrase down to simply:

have mercy

The link above will take you to a crowdsourced thesaurus called **Power Thesaurus." If you can't link to it, some choices from the list that fit the context you provided would be:

acquiesce | cool it | ease up on/go easy on | give some slack | relax | be understanding

To this, you can the add the modifier "little," which would give you expressions such as:

"be a little acquiescent" or "cool it a little bit"

and so on and so forth down the list.

What the author of this paragraph seems to be suggesting is that even though the bankers' usual methods of analysis regarding inflation and employment are not currently evident (key clue phrase here is "disappearance of the Phillips curve") bankers need to be a little understanding because "inflation is hard."

In the following paragraph (which is important, so I will add it here):

By the way, the oft-repeated mantra that "inflation expectations are anchored" offers no solace. In fact, it makes the puzzle worse. The standard Phillips curve says inflation = expected inflation - (constant) x unemployment. Variation in expected inflation is usually an excuse for a Phillips curve failure. Steady expected inflation means the Phillips cure [sic] should work better! (But beware that anchor. Is it anchored, or just not moving?)

he gives details that suggest that bankers shouldn't automatically discount the Phillips curve or assume that the model has failed. He's suggesting that the bankers examine it more closely. Perhaps the model isn't faulty; perhaps their understanding of it is. The author is asking them to give the Phillips curve a chance because it might make more sense than they can realize at the moment. In other words ... have mercy on it.

Answer 2

I think it can be rephrased as this:

And if central bankers are a bit befuddled by the utter disappearance of the Phillips curve (no discernible relationship, or actually now a relationship of the wrong sign, between inflation and unemployment), in this case have a little mercy/forgiveness. Because modeling inflation is hard.

So "have a little mercy" is equal to something like "do not expect too much", or "do not judge them bad" here.