Does Giles' refusal to name his informant help or hurt his credibility? Explain your answer.

 This above all: to thine own self be true,

And it must follow, as the night the day,

Thou canst not then be false to any man.

Explanation:

He's telling Laertes that the best thing he could really do, out of all of the advice he had already given, was to stay true to himself because that leads to less falseness to others. Allowing his to be a better person for it due to his honesty rather than a successful person for his falseness. Tying in with the theme that you should take care of and know yourself first in order to be able to attend to others at the best of your abilities later.