Most adults have no memories from before age three or four, even though toddlers clearly remember what happened yesterday. This is “infantile amnesia”. One leading idea: the still-developing brain, especially the hippocampus, can't yet lock those memories into long-term storage. Your earliest years happened; you just can't retrieve them.
Every day, your kidneys filter around 180 liters of blood plasma, about a bathtub's worth. Yet you only have about 3 liters of plasma, so it passes through your kidneys some sixty times a day. Over 99% of the filtered water is reabsorbed, leaving just one to two liters of urine.
A 70 kg adult is made of about 7 × 10²⁷ atoms, or seven billion billion billion. The observable universe is thought to hold on the order of 10²² to 10²⁴ stars. Even with the high estimate, you contain thousands of times more atoms than there are stars in the entire visible cosmos.