I had a Yorkie that might be described as cautious more than timid, he would let my Westie take the lead in situations that were out of the ordinary. If he didn't like a situation he would just walk the other way. The most independent thinker had to be my Cairn, to the point of being bullheaded. I think all terriers have a bit of that independent thinker thing going, due to the nature of the breed. If you can get them to think what you want them to do is their idea they listen pretty well.