This is the 'Regress of Reasons'. One response to the regress is scepticism. One accepts that the regress can never stop, so nothing can be known because no-one can ever ultimately be justified in a knowledge claim. The CF theorist is not so pessimistic. According to CF the account of knowledge above applies only to 'inferential' knowledge.
Some knowledge is 'non-inferential'.
That is, one is justified in claiming to know without evidence. In fact, such knowledge is the basic evidence on which all other knowledge is founded. One idea is that it is justified by being 'certain'. Being 'certain' is a complex matter. It is not meant to indicate merely psychological confidence.