When buffalo were still common in North America, Native American hunters learned a trick to hunt the herd animals. Buffalo don’t look up when moving as a group. In fact, if a few buffalo in a herd were startled into running, the entire herd would charge, even if most of the buffalo had no idea what they were running from.
The Native American hunters learned that if they encouraged a few buffalo to start running towards a cliff, the entire herd would run off the edge. The buffalo followed the group thinking, and couldn’t stop themselves–even when it meant their own deaths.
Although you’re probably not gullible enough to run off a cliff, it’s easy to stop thinking for yourself. It’s easy, because you don’t realize when you’re doing it. Thinking for yourself takes effort, and it’s easy to be tricked into going over the edge.