What are your two greatest weaknesses?

When answering a question like this, interviewers are not looking for the exact right answer but your non-cognitive ability to reflect and see potential for improvement.
An answer such as my test scores or my 1500m athletics time doesn't demonstrate reflection of the way your personality affects real-life scenarios and how these could be changed and may come across as possibly quite shallow, or that you have not thought the question through at all
An answer such as my ability to accept failure, possibly with an example, shows insight into your weaker areas of your approach to life as well as a keenness to improve on them (as you have reflected on this skill)