This line comes at the end of Hamlet's famous "to be or not to be" soliloquy. After comparing the merits of one versus the other, Hamlet concludes that people usually choose life over death, potentially in the form of suicide, because they fear what comes after death. The thought, or "the conscience" of the unknown "makes cowards of us all," and we have second thoughts about making the impulsive decision to end our lives:
And thus the native hue of resolution
Is sicklied o'er with the pale cast of thought,
And enterprises of great pitch and moment
With this regard their currents turn awry
And lose the name of action.
Hamlet is not considering suicide, but he is clearly a tormented young man. This soliloquy is one of the most soul-searching moments in Western literature.