What is "break in" and what difference does it make? In amps? Preamps? Speakers? More?

@asvjerry I'm getting good answers here and realizing a thick skin may be necessary. I'm a college professor, of philosophy. I am not at a highly selective school and many are first generation college students. Every semester faculty at my school are asked very similar questions by new students. We find that even answering questions we've had before teaches us something, so long as we try to appreciate the perspective and practical motivations of the student. It is professional suicide to blame the learner. 

the mention of how this has been discussed many many times is not a criticism of you, but letting you know if you look through the threads there are already thousands of responses...my experience is that most of my equipment and cables have improved with a few hundred hours of playing time...and all bought with return privileges extending way past the break in period...

I hear you. Thanks! I guess I was also wanting to try a little engagement with folks in the group. There are very few people I know who are into audio, it's good to try a few interactions.

This horse has been flogged to death many times but I'm still going to put in my $.02.

The only relevant point is that you shouldn't make a judgement on sound quality when you first hook up a new piece of gear whether it's a piece of electronics or speakers. If it's the gear changing sound or your brain adjusting to the sound of the new gear - it doesn't matter. Just hook up the damn thing and run it for a few weeks before making a final judgement.

I'm a pretty strong skeptic about things like break-in but I have absolutely heard the effect myself. I'm perfectly willing to admit that my brain is actually what "broke-in" but whatever. Something happened to change what I heard (or think I heard) - that's all I know.

I am always wondering if anyone ever made the following test: take two identical units of cable, subject one to the alleged burn-in, then do blind testing on both attempting to tell the difference.