I guess to be in politics, one cannot be sitting on the fence at all.
It is either A or B. No in between.
There isn't anything in between A or B.
So one must decide. Responsibly and quickly.
But what happen when after the joining party A, the person realised that he had chosen the wrong boat? It is actually heading down the rough water and the captain was just sitting leisurely looking after a few of his fishing rod and no one is navigating the boat.
Can he go up the fence again, or he just swim his way up the other available boat?
In local political arena for the past forty years, there had been a lot of jumping in and out. Changing boat and changing course.
Does this make the person lack leadership attributes? Perhaps.