What does the "pale cast of thou

Reading Comprehension: Read the quoted parts carefully and answer the questions in English. "And the native hue of resolution 
Is sicklied o'er with the pale cast of thought"
What does the "pale cast of thought"stand for?
【正确答案】：

THE EXCESSIVE CONTEMPLATION THAT PARALYZES OUR ABILITY TO TAKE NECESSARY ACTIONS AND RUNS MEN INTO COWARDS.