Burden of proof falls on the party who would lose if neither side produced evidence, shifting with pleaded facts. The provision establishes that the burden of proof lies on the party who would fail if no evidence were given on either side; thus a plaintiff seeking land from a possessor bears that burden because possession would prevail without evidence, while a defendant alleging fraud in an otherwise admitted bond bears the burden to prove fraud because, absent evidence, the admitted instrument would support the plaintiff's claim.