That is a deep question. Some might say love.
Answer: the donkeys they rode on their exepeditions into the countryside
they...acquired the nickname "the donkeys"
Explanation:
1)help your parents
2) do your homework that given by your teachers
3) going to the tuition class
Polonius is using his daughter to spy her conversation with Hamlet. He teaches how to act naturally, how to walk and pretend that she is reading.
In that last phrase, he is saying that we humans often act in deceitful ways, for which we are to blame.
He admits that he is making a mistake, in teaching that kind of behaviour to his own daughter.