What is the difference between 'certain' and 'specific'?

For example, what would be more appropriate to use and why:

'This guy has a certain list of skills' or 'This guy has a specific list of skills'

I'd appreciate any other examples that would be helpful in understanding the difference between the two.

Thank you

Solution 1:

This guy has certain skills.

The speaker has only seen partial evidence of the guy's skills; he may or may not be aware of all of them, or their overall quality. He is certain the guy has skills; it's what they all are that he's not too sure about.

This guy has specific skills.

The speaker is only referring to those skills he's aware of; he's absolutely certain the guy has them. He can specify them.