  Fine-tuning pre-trained models have achieved impressive performance on
standard natural language processing benchmarks. However, the resultant model
generalizability remains poorly understood. We do not know, for example, how
excellent performance can lead to the perfection of generalization models. In
this study, we analyze a fine-tuned BERT model from different perspectives
using relation extraction. We also characterize the differences in
generalization techniques according to our proposed improvements. From
empirical experimentation, we find that BERT suffers a bottleneck in terms of
robustness by way of randomizations, adversarial and counterfactual tests, and
biases (i.e., selection and semantic). These findings highlight opportunities
for future improvements. Our open-sourced testbed DiagnoseRE is available in
\url{https://github.com/zjunlp/DiagnoseRE}.
