I have the shortest half-life of all the elements. I am decaying into nothingness.
Keep on looking for Astatine. I know you will be able to see him.
But Indium will never be able to see me. Because I also have a very short half-life, I am very rare, so there can never be a visual model of me.
The only way scientists know I exist is because sometimes other elements decay and become me. By knowing how many parent elements there are, scientists can find about how many isotopes of me there are.