Origin
A photograph purportedly showing a group of sheep squeezing through a gate despite there being no fence is frequently shared as an example of "the trap of thinking":
A herd of sheep is leaving the stall. There is no fence, only the gate...
"The Trap of thinking"
However, whether or not the sheep are stopping to think about it, there actually is a fence in the above-displayed image.
This image was taken by Australian photographer Scott Bridle in 2012, and shows a group of sheep passing through a gate at Brenda Station. While the encircling fence may be hard to see in this particular photograph, fence posts are clearly visible in a higher resolution version. Furthermore, fenced-in sheep can be seen in two other images Bridle took of Brenda Station in 2012:
Finally, Carolyn Ferguson of Scott Bridle Photography confirmed to us that there was indeed a fence in this photograph:
Yes, there is definitely a fence.