Jerry the non working goat....

[Sanhestar]

there are some goats that have a hard time leaving home/herd. I also found that two goats are more alert/ready to spook when out then four or five - safety in numbers. I always take four goats out and my regular packing string consists of six (although I have no need to pack that many).

Jerry might be a timid type of character who feels unsafe/scared when out on the trail. You could try how he behaves when you go out with all four goats, if he's braver then.