1. Being refused
A package returns mainly because it has been refused by the person at the address. It could be a family member who isn't aware of the package is what you've ordered or a friend who has no idea that it is a gift for him/her.
2. Insuffiecnt/wrong address
Sometimes couriers would automatically return packages with insufficient/wrong addresses, such as no apartment number, wrong postal code, or even no access to enter the apartment. Please make sure you have left a valid and sufficient address.
3. No pick-up for a long time
If the package is delivered to a self-pickup point for some reason, such as recipient's require, or delivery service unavailable at the moment and no one comes to claim for it. The package will be returned after 7-30 days.