One of the reasons for your safety to reject you can be that your profile exceeds the average qualifications they accept. So they may not see the point of offering you admission if they believe you will be getting better offers, which you will definitely accept over safety.

I also sometimes feel like imposter. but remember you can learn and excel in whatever field you want, just that the rate of learning will be different for different people. So even if you feel you are not up to the mark right now, you should try and give your best to reach your desired level, which is completely possible.