The shepherds, according to what Richard Beck suggests, would have a psychology similar to that of herding societies, ie, they would be -according to some academic studies- more violent and retaliatory than the peaceful farmers. The psychological difference between the herding and farming societies seems easy to explain. It is hard to steal from a farmer. The harvest is only ready for some part of the year and even so, during one night two thieves would not be able to get much. Conversely, two men can very easily still the sheep from a shepherd or the caws from a ranger. The shepherds have to stay vigilant day and night all day round. If you had all your savings, and stock options in a pile in your yard, you would surely watch it closely! Thus, because of these differences, the herding societies develop a "culture of honour" in which retaliation is very important, while the farming cultures would be less violent and more peaceful.
Now, if we look again to the scene of the shepherds, our shock and amazement cannot but increase in the light of this explanation. The shepherds, after hearing the good news of a new born child, and after listening to the heavenly host proclaiming peace on earth, they decide to leave the sheep and go to look for a baby! The gospel tells us that they hurried to see the baby, thus, even if nowhere we get explicitly that they left the flock unattended, it is quite logical to assume so. Were they crazy, the shepherds, to do this? I like to think that this was one of the miracles of the Christmas night. For one day, they stopped being afraid and were filled with the good news of the Kingdom that is coming, as it were already there. They believed the angels saying "Peace on earth".
Finally, the story of the shepherds reminds me of another story, the parable of the good shepherd, the one that leave ninety-nine sheep! just to go for one sheep that is lost. So great is the love of God that our way of leaving becomes not of this world.
In that region there were shepherds living in the fields, keeping watch over their flock by night. Then an angel of the Lord stood before them, and the glory of the Lord shone around them, and they were terrified. But the angel said to them, ‘Do not be afraid; for see—I am bringing you good news of great joy for all the people: to you is born this day in the city of David a Saviour, who is the Messiah, the Lord. This will be a sign for you: you will find a child wrapped in bands of cloth and lying in a manger.’ And suddenly there was with the angel a multitude of the heavenly host,praising God and saying, ‘Glory to God in the highest heaven, and on earth peace among those whom he favours!’
When the angels had left them and gone into heaven, the shepherds said to one another, ‘Let us go now to Bethlehem and see this thing that has taken place, which the Lord has made known to us.’ So they went with haste and found Mary and Joseph, and the child lying in the manger.
This post was very inspired and much followed Richard Beck´s one, that you can find here.