Why is implantation in the endometrium critical for the embryo's survival?

An embryo can only attach to endometrial tissue, even in ectopic pregnancies there is usually a history of endometriosis. however, endometrial tissue is outfitted to sustain and provide a housing unit for a pregnancy, and offers adhesive proteins for the egg to attach to. if no endometrium, then no attachment, then no pregnancy.

Well if you pick a machine to work on and that's gonna be your exercise if you don't stick to that machine your muscle strength your muscle mass rather will change because you haven't been doing it you change something in your exercise routine which changes your body's form of dealing with things for example you might become weaker or stronger depending on what kind of exercises you do in whether or not the machine you picked actually your muscles grow.