An unsound argument is never rationally persuasive. The force of a sound argument is the force of consistency or non-contradiction. A sound argument makes clear to the hearer or reader that to accept the reasons offered while not accepting the claim or conclusion is to be in contradiction with yourself.
Every argument has reasons that support a claim.
If there are no reasons, then, though it may appear to be an argument and persons may take it to be an argument, it is not. Reasons which fail to meet one or more of these criteria weaken or destroy the overall soundness of the argument. This is the relationship between the reasons and the claim. A good or valid inference is where the reasons, were they true, would be sufficient to establish the claim being true. It is where the claim clearly follows from the reasons.