There are many places where bugs can be found:
1. By the developer when they first write the code.
2. By the developer when they’re trying to get the code to work.
3. By another developer or tester on the team.
4. As part of the larger test of the product.
5. By an end user.
Oops, large part of the number of Korean companies still have no professional testing team. Therefore in most cases, the bugs are to be found in case #5.