Who Is It?

Original Text: 
Albert Durrant Watson, The Wing of the Wild Bird and Other Poems (Toronto: William Briggs, 1908): 87. Internet Archive.
1If he has to, he will not,
2    He will if he mustn't;
3He does if he shouldn't
4    And should if he doesn't.
5If he can, he won't try it,
6    If he cannot he wants to;
7Whatever's forbidden,
8    That's just what he's drawn to.
9You'd have him a sage,
10    Then he'll talk like a fool;
11He's as cross as a saw-horse
12    And acts like a mule.
13"Who is it?" you ask,
14    I should like to know, too,
15But it's your private task
16    To take care 'tisn't you.
RPO poem Editors: 
Ian Lancashire
RPO Edition: