Why no “Break in” period?

Exactly, TIM was the same situation. We all heard something wrong then they finally figured out what it was and how to measure it. But this is not what we are talking about here. We are talking about differences people hear when there is nothing wrong. We are not talking about what the ear hears. We are talking about how our central nervous systems interpret what the ear is hearing and that is a far more complicated and plastic issue and it seems in this forum modulated by ego. Many of the explanations are being devised by people who have no idea what they are dealing with or talking about with an unfortunately high level of arrogance. What is even more interesting is that the people who are closest to the truth are attacked the hardest. 
If people do not want to understand how their brains can trick them and spend their money on worthless garbage that is their prerogative. Do not think this is the search for the truth. It is more or less the re enforcement of mythology. 
Geoffkait, Einstein was a "Newbie" when he came up with the theory of relativity. 

If you don't believe your ears, maybe it's easier to believe your eyes.  I've owned several PS Audio Power Plants over the years and I always break them in using my TV since I hate the break-in process and watch more TV than listen to music.  The first time I did this the picture initially looked crap- colors were oversaturated and the tonal balance was off.  But after a a number of days days everything started to change and the improvement was obvious- a more three-dimensional picture, better shadow detail and more subtlety in colors etc.  

Since music is constantly changing we tend to play the same track over and over and it's difficult to know if our memory is fooling us sometimes.  But a picture is somewhat steady state, say at a live football game.  You'll get the same camera shot of the same scene for hours and it's very easy to analyze the picture quality.  The first time I used my TV in this manner I made the mistake of changing my settings after a day or two, only to have to do it again a few days later once the Power Plant settled down.  

I was already well aware of the break-in requirement in audio because I've had some components with very long and painful break-in period.  But the TV was the most dramatic proof that something was changing in the electronics.  Since I'm a mechanical engineer by training, I don't believe in unicorns or alchemy, but I do believe that electronics require break-in, and the more revealing they are the more likely you'll hear the difference.

My Hana el cartridge sounds nothing like it does now at least 15 hours to break in.  easy to hear the difference... voices were to big not natural ,a friend said so too. Then after 15 or so hours everything fell into place . He came back a week or so later and said that’s better .  And all I did was play records.

Fedie,
Same experience here with a new benz cartridge I'm breaking in. Dynamics improve, soundstage expands, imaging improves. I'm on about hour 50 now. 

Definitely something more than subjective acclimatization, albeit with no objective confirmation method. When a process unravels over time before your ears, with all other variables (local power demands, ambient atmospheres, etc.) controlled by repetition, the explanation must be a physical adaptation of the signal passageway itself, from raw flat asphalt (new Cardas copper) to hard biased pavement. Because of the traffic, and maybe the nature of the traffic. Very different from unicorns or magic fairies in the sky. Too bad there's no evident way of making bombs or curing cancer out of it, or maybe we'd know by now the mechanism by which this occurs.