Answer:
1. You don't have enough experience for the job.
2.There was a better candidate for the job.
3.You didn't take an interview seriously.
4.Your not professional enough.
5.You might have a criminal record and this job you are applying for doesn't want someone with a bad record.
6.You don't have any recommendations.
7.Your previously bosses say that you aren't a good employee.
8.You aren't punctual. (on time)
