As Joel Preston says:
-Sheep are stubborn. Sheep can get easily lost because they tend to go their own way. Like sheep, believers have a tendency to go their own direction rather than follow the divine Shepherd's plan. So Ps 119:176 says, "I have gone astray like a lost sheep; seek thy servant; for I do not forget thy commandments."
From Rick Crandall's Sermon "Part 2- Living in the Overflow of the Lord"