Richard Alpert and Doubt [LOST]

As a quick followup to this morning's post on doubt, last week's LOST had an interesting take on the role of doubt.  Richard Alpert has (presumably) been doing Jacob's bidding for a few centuries and once that role is taken from him (I'm being intentionally vague for fear of spoilers), doubt consumes him.

Here's the exchange I'm talking about:

RICHARD: What I'm talking about Jack is that...Jacob touched me, and when Jacob touches you... well it's considered a gift... except it's not a gift at all. It's a curse.
JACK: Why do you want to die?
RICHARD: I devoted my life, longer than you can possibly imagine, in service of a man who told me that everything was happening for a reason, that he had a plan, plan that I was a part of, when the time was right that he'd share it with me, and now that man's gone so...why do I want to die? Because I just found out my entire life had no purpose.

To Alpert, certainty was the crutch of faith that he leaned on, certain belief in his role.  But when that certainty was taken away, he felt lost and alone, going through a dark night of the soul.  It seems like a parallel journey to people who subscribe to determinism, or that every action is willed by God to have a purpose (ie. purpose-driven, perhaps?). When the pieces don't fit together, how does one keep their faith?  Or is it better to allow it to die and be resurrected anew stronger than before after the dark night has passed?