Matthew 20:10

And when the first came, they supposed that they would receive more; and they likewise received every man a shilling.

The expectation of those men was groundless because they had firmly agreed with the householder for a shilling a day. Their expectation of more resulted from the comparison they made between themselves and the ones who came to work later. It was that very thing, the envy, jealousy, and petty attention to little differences - it was all that Jesus was trying to remove from the apostles' hearts. The perverse and sinful judgments and rankings of themselves among themselves, with the consequent jockeying and maneuvering for position and advantage - these things constitute one of man's most shameful and hurtful patterns of behavior. Paul paid his respects to that vice in these words:

For we are not bold to number or compare ourselves with certain of them that commend themselves: but they themselves, measuring themselves by themselves, and comparing themselves with themselves, are without understanding (2 Corinthians 10:12).

The workers first employed fell into that same foolish trap. As a result, they developed a conceit that turned to outrage when the householder made them equal to the latecomers.