Fertilization is a hallmark event of sexual reproduction marked by the fusion of male and female gamete to form zygote. It is a highly complex, yet a robust process that is intricately regulated by various signalling molecules. A healthy fertilization is determined by the quality of zygote which is contingent on the health of egg and sperm. The relationship between infertility and gametic health can be reciprocal. On one hand gametogenesis has to be dynamic and unremitting to sustain the reproductive health, while on the other hand it has to be error free for proper embryonic development. Complex cellular interactions make gametogenesis highly vulnerable to extrinsic as well as intrinsic intrusions. Molecular disparities during these phases may result in complete fertilization failure. Present review provides an overview of the regulation of gametogenesis, determinants of healthy gamete, players at fertilization window and what may go wrong during the development of zygote to embryo leading to implantation failure. We have outlined different 'windows' of vulnerability during gametogenesis supported by evidences affecting the fertility potential of both the partners.