Why can it be said that a recessive allele can remain hidden in the phenotype of an individual and revealed only when manifested in homozygosity in the offspring?

A recessive allele can stay hidden because it does not manifest in heterozygous individual that is it may be present in the genotype but not expressed in the phenotype. While this allele is transmitted to the offspring and forms homozygous genotype with another recessive allele from other chromosomal lineage the phenotypical characteristics that come out reveal its existence.