What is due to us (3)

Efforts are made to persuade Hamlet and Mrs. Dashwood to put aside their sensibilites in the name of sense. Claudius give Hamlet what is, in fact, very good advice about excessive mourning below. Remember that Hamlet does not yet suspect his father is murdered. The only thing that bothers him is that life is moving on and his father is being left behind and that offends his sensibilities.

And if that were all there were to it, then every word of Claudius's here is would be right:

But to persever 295
In obstinate condolement is a course
Of impious stubbornness. 'Tis unmanly grief;
It shows a will most incorrect to heaven,
A heart unfortified, a mind impatient,
An understanding simple and unschool'd; 300
For what we know must be, and is as common
As any the most vulgar thing to sense,
Why should we in our peevish opposition
Take it to heart? Fie! 'tis a fault to heaven,
A fault against the dead, a fault to nature, 305
To reason most absurd, whose common theme
Is death of fathers, and who still hath cried,
From the first corse till he that died to-day,
'This must be so.' (Act 1, Scene 2)