different between verification in principle and verification in practice?

Answer 1

Verify your own existence on paper using "logic."
You can't.
But using "logic," you can verify someone else's existence.
That means to me...
It is all about you...
Not me...

Answer 2

I don't know that there's really any difference, except that verification in practice can sometimes be trickier.

One can verify something in principle by going through all the logical steps needed. In practice, one would also need to follow good scientific methodology, being careful to eliminate biases, eliminate anything extraneous, not do sloppy work, etc.

An analogy might be writing a computer program as a flowchart to get the general idea of how it should work, versus writing it in actual computer code, making sure you don't make any syntax or logical errors.

P.S. To JackZen, how to verify your own existence on paper:
1. Write down anything on paper.
2. Would you have been able to write it, or read it afterwards, if you didn't exist? Ergo, you must exist. "I think, therefore I am."