1.The earrings were damaged when they arrived.
2.The Post Stud Earrings Damaged
It's not uncommon for stud earrings to come apart. All that's necessary is E6000 glue or Aleene's Ultimate Glue. Leave the glue to set for several hours - until it's crispy, not soft. Use the tip of a razor blade or stanley knife to raise an edge of the glue outside the cup. Take care not to scratch the earrings. With luck, you can now peel off the glue around the cup. A fingernail is ideal for flicking off anything that remains.
3.The hoop earrings are too loose.
It may become loose
after using it many times.
In the case of hinged hoop earring
earrings, they were tension set, rather
than pin set, which is why it eventually
came loose. In the future, you just need a pair
of pliers to press the outer sections together from
time to time to ensure they don't release the post.