In a past discussion of the conflict between Ya'akov's fear and the needs for bitachon I described the Abrabanel's insight which my wife pointed out to me as a "realisitic model of bitachon". Ya'akov was preparing for battle with his brother. Abarbanel writes that someone who has no fear of battle is a fool, not a ba'al bitachon, because such a person does not have a sense of the value of human life. Precisely because a hero is fully aware of what stands to be lost, yet nonethless conquers fear and enters battle, is he considered a real ba'al bitachon. Trust in G-d does not mean overlooking the dangers posed by reality or being fearful of the consequences of failure. Bitachon means pushing ahead despite those fears and consequences.
The thoughts are always well meant, but going over to someone who just found out they have an illness, lost a job, or some other tragedy and telling them "Don't worry" is not going to make them feel any better even if you insist that G-d will make things out. Worry full well! But despite that worry, be confident that G-d is still with you.
This is my favorite approach to the topic, and it is an approach that I found echoed in a teaching of the Ishbitza. Going back to the gemara, the idea of shema yigrom hacheit which we find by Ya'akov is presented in the context of the gemara telling us that David haMelech would arise every night at chatzos to ponder his fate. Although he was a "chassid", righteous beyond reproach, he nonetheless feared as well shema yigrom hacheit, a fear which the gemara cites Ya'akov as the model for. Why did he arise precisely at chatzos to ponder this message? Explains the Ishbitza, it is humanly impossible to reconcile fear and bitachon. If one is truly confident, one has no fears; if one is afraid, one lacks bitachon. Yet, these emotions coexist in each of us. The key is to maintain a balance between them. We must arise at chatzos, the precise midpoint, or we risk faltering.
The gemara continues on the nexy amud to tell us that one who is someich geulah l'tefilah by ma'ariv is a ben olam haba. The Ishbitza reads this gemara as hinting at the same theme. For the ba'al bitachon, G-d's geulah, redemption, is always at hand. Yet, in the darkness, when no light of hope can be seen, our fears lead us to call out in prayer to G-d. Logically it is impossible to explain how these emotions can coexist. If redemption is at hand, then need we pray with all our might?; if we pray so fearfully, are we lacking in confidence that G-d will act only for the good? We flip-flop between theses different poles, because only a ben olam haba, outside the constraints of this-worldly reason can possibly manage them simultaneously. Yet, that process of flip-flopping from one to the other, of using one as the springboard to the other, is precisely what we are charged to do.
In the Ishbitza's model there is no denying or resolving the contradiction between yirah and bitachon. Akin to the Kierkegaardian knight of faith, the human condition is one of paradox.