What is the most overlooked consideration?

Never thought I would say that, but power management is a key consideration. Outlets, power cords and power plants can transform the sound of a system. I was very skeptical until I experimented with them. No need to go nuts, however. Just need clean stable power. Similar experience with external power supplies vs internal ones.

Buying equipment you can buy, try in your listening room with your equipment with the ability to return for no or little money if you’re not happy.  That involves Customer service and warranty.  I see so many questions online after people have bought equipment and can’t get help from the manufacturer or are looking for where to get gear repaired.  

Very interesting and thought provoking answers. It’s a way the Audiogon forum can actually help, by sharing ideas, solutions and opinions. It is possible that threads do not have to be filled with arrogance and personal attacks. For those who have a complimentary stereo component or accessory the WAF is another overlooked consideration. No offense intended. Offered by @aewarren and I am in agreement.

+1 The room.

2.) Psychology. Does it really sound different, or do I only think it has to sound different? Is it better, or do I think it has to be better because I spent more?

The simple answer is:

Understanding how a component produces music which comes down to the build and the parts used like the transformer, power supply design and capacitors used, etc.

Without knowing this, you are just buying one brand or another.