The nice thing about the shower in the hotel room where I recently spent a few days was that the enclosure was quite long, long enough so that towels hung up at one end of it were a safe distance from the shower head at the other end. Also, and more important, long enough so that I could use the shower control at one end of the enclosure while a safe distance from the water at the other end whose temperature I was adjusting. That eliminated the usual problem of getting frozen or scorched while getting the water to my preferred temperature.
The not nice thing about the shower was that it took a long time for the temperature of the water to respond to a change in the control, which made the whole process of adjusting the shower to my preferred temperature more difficult than usual.
It eventually occurred to me that these two features were connected. The farther the control is from the shower head, the longer the pipe between them. The longer the pipe, the longer it takes for the changed mix of hot and cold water to get from the control to the shower head, hence the slower the process of adjustment. The feature I did not like was part of the cost of the feature I did like.
This is one example of a general point. Consider any system—a shower, a car, the human body—that has been optimized. If changing the system in some way, in my example moving the control farther from the shower head, produces a benefit, it must also produce a cost—otherwise the change would already have been made in the process of optimizing the system.
The human body has been optimized by evolution. But the purpose it was optimized for, reproductive success, is not my purpose. Hence there might be changes to be made that are to me unambiguous improvements—dollar bills lying on the pavement to be picked up. Still, it is prudent to suspect any obvious improvement of a downside.
Many years ago my father decided to stop using the phrase "there is no such thing as a free lunch" on the grounds that it was not literally true—consider consumer surplus and producer surplus. If someone pays me a thousand dollars to give a talk I would be happy to give for free, I have just gotten a thousand dollar free lunch.
His substitute: "Always look a gift horse in the mouth."