Macs will not connect using Migration Assistant

Yes, I finally just did that and started the backdown from the Time Machine backup. While Apple has tried to make this process transparent, it is not. And why did I get 10 hours of transfer with the Ethernet cable before it stalled even though I did not tweak the configuration? And, why don't the instructions for using Migration Assistant warn about the extra setup requirements using Ethernet cable? I am still not clear about the repeated messages I am getting to authorize the backdown using the Time Machine backup. It will be interesting to see what I get in 24 hours or so when the backdown is completed.

It would be nice if someone could write a comprehensive document detailing the various ways to transfer data to a different machine, including all the things that can go wrong with each method.