Fixable: “I get nervous when speaking in front of large groups.”
(You can get better through practice and learning new skills — and this is a common development area.)
Harder to fix: “I am very shy and often have trouble speaking up in meetings.”
(While there’s nothing wrong with being shy, an interviewer could assume that the candidate would have trouble collaborating in a team environment. This is a preference or personality quality that would be more difficult to change.)