Final answer:
The main character's weakness as a knight in 'The Physicians Tale' is highlighted in line 3. Virginious may also lack empathy or understanding for others' suffering.
Step-by-step explanation:
In 'The Physicians Tale', the line that highlights the main character's weakness as a knight is, 'He passeth by; and his weak spirit fails' (line 3). This suggests that the knight lacks the courage or strength to face the hardships and struggles of being a knight.
Other weaknesses of Virginious are not explicitly mentioned in this excerpt. However, based on the given information, we can infer that he may lack empathy or understanding for the suffering of others, as indicated by the line, 'To think how they may ache in icy hoods and mails' (line 4).