Put no faith in the promises of Princes...

History of Richard III, Act IV, Scene 2

In fairness, Richard is annoyed at Buckingham for not immediately agreeing to assist in murdering Edward (a dishonourable act if there ever were one). Richard's favour depends on "what have you done for me lately". Still, the point is Princes can promise but they do not often deliver:

Duke of Buckingham. My Lord, I have consider'd in my mind. The late demand that you did sound me in.

Richard III. Well, let that pass. Dorset is fled to Richmond.

Duke of Buckingham. I hear that news, my lord.

Richard III. Stanley, he is your wife's son well, look to it.

Duke of Buckingham. My lord, I claim your gift, my due by promise,
For which your honour and your faith is pawn'd;
The earldom of Hereford and the moveables
The which you promised I should possess.

Richard III. Stanley, look to your wife; if she convey
Letters to Richmond, you shall answer it.

Duke of Buckingham. What says your highness to my just demand?

Richard III. As I remember, Henry the Sixth
Did prophesy that Richmond should be king,
When Richmond was a little peevish boy.
A king, perhaps, perhaps,—

Duke of Buckingham. My lord!

Richard III. How chance the prophet could not at that time
Have told me, I being by, that I should kill him?

Duke of Buckingham. My lord, your promise for the earldom,—

Richard III. Richmond! When last I was at Exeter,
The mayor in courtesy show'd me the castle,
And call'd it Rougemont: at which name I started,
Because a bard of Ireland told me once
I should not live long after I saw Richmond.

Duke of Buckingham. My Lord!

Richard III. Ay, what's o'clock?

Duke of Buckingham. I am thus bold to put your grace in mind
Of what you promised me.

Richard III. Well, but what's o'clock?

Duke of Buckingham. Upon the stroke of ten.

Richard III. Well, let it strike.

Duke of Buckingham. Why let it strike?

Richard III. Because that, like a Jack, thou keep'st the stroke
Betwixt thy begging and my meditation.
I am not in the giving vein to-day.

Duke of Buckingham. Why, then resolve me whether you will or no.

Richard III. Tut, tut,
Thou troublest me; am not in the vein.