So much of the judeo-christian belief system, but especially the beliefs of Jehovah's Witnesses are based on Ad Hoc arguments. The bottom line with them is - "You just have to have faith."
I found the true definition of "faith" being - Accepting something to be factual without any evidence or proof.
When Witnesses condemn one of their own as being "weak in the faith" what they are actually saying is that the individual requires too much evidence to act the way the organization expects them too. In short, if a Witness were truly faithful they would be acting like Armageddon is coming tomorrow.