Answer:
Be true to yourself
Explanation:
This sentence by Polonius is continued with:
'<em>And it must follow, as the night the day, Thou canst not then be </em><em>false</em><em> to any man.'</em>
This is important because it shows the (moral) effect of being true to yourself on others. In other words, if you live your life in a true and honest way, your social life will be likewise.
There is another side to these lines: it implies that you should also be true to your own caracter or personality, which is the essence of you as a person. This has led to many phylosophical discussion and questions such as:
<em>Should I be true to myself when I hurt somebody else?</em>
But I am afraid the answer to this question is not an easy on...