Some people look to God for justice; others pray to Him for grace.
Both characteristics are in God, of course, but they are not the same thing. Fairness is getting what you deserve. Grace is getting what you don't deserve.
The Parable of the Laborers in the Vineyard causes headaches for many Christians. There is just something that seems so...unfair about it all. Those shirkers who only put in an hour are paid the same as those who worked all day? Where is the justice in that?
And yet no one is really mistreated here. Those who worked a full day get a full day's wage. They receive what they agreed to and get what they were promised. There is no injury. It's fair. Case closed.
However, there are others who receive not fairness, but a glorious unfairness! They receive a full day's wage for working only an hour. That's not justice - that's grace!
How you respond to this parable probably depends a lot upon how you see yourself in it. If you consider yourself to be one of those who has "slaved away" for God through most of your life, you may relate more to the consternation of the full day workers. If the circumstances of your salvation mean that you were saved later in life, however, you may feel a deeper kinship with the joy of the eleventh-hour workers.
There's a commonality here with the Parable of the Prodigal Son, who also received a gracious welcome that he did not deserve, much to the chagrin of his responsible older brother.
Stepping outside the realm of parables, we see this teaching come to a flesh-and-blood realization with Christ's acceptance of the thief on the cross. In literally the last moments of this man's life, he enters into the grace of his Lord. Will we protest at that unfairness, or will we marvel at that grace?
Personally, I'll take that kind of injustice any day!