Many patients who undergo IVF for pregnancy because of the female partner’s fallopian tube, ovulation disorder or the male partner’s low spermatozoa often have the question: Why do the embryos sometimes not get pregnant after being transferred into the uterus? Isn’t the sperm and egg already united to form an embryo? In fact, pregnancy is far from simple, and the union of sperm and egg is only the first step in a long journey. The quality of the embryo and the tolerance of the endometrium, as well as the synchronization of the two, play a decisive role. It is like the relationship between seed and soil, where the embryo is the seed and the endometrium is the soil, and the match between the two means that the seed needs to be sown at the right time. A good quality embryo is like a good seed. Currently, the morphology and developmental rate of the embryo are mainly evaluated by means of a simple and non-destructive method, but it is still not possible to accurately predict the developmental potential of the embryo. The quality of the embryo is influenced by the patient’s own ovarian reserve capacity, in addition to the timely and precise administration of medication during the superovulation process. This is why many older patients with low ovarian function are unable to obtain quality embryos after multiple egg retrievals. A good seed cannot be obtained without fertile soil. The endometrial tolerance, which is the ability of the endometrium to accept embryos, is commonly evaluated clinically by vaginal ultrasound examination of the thickness and morphology of the endometrium. It is now accepted that a minimum thickness of the endometrium (usually 7 mm) is required for normal embryo implantation in assisted reproduction treatment. Of course, there are times when good quality seeds placed in fertile soil do not grow because there are many unknown reasons that affect embryo implantation. The developmental potential of the embryo can only be determined by the ability to conceive after the transfer.