But there is also free will. Thus the decision to have faith is dependent on one's will and it is part of the nature of the world to have this faith tested many times. But if one falls from faith because of some test and then his faith becomes less, then reality will conform that that lesser amount of faith. And then when things stop going right, then one's faith gets even less. And then things get worse and worse because they have to conform to his lack of faith.
At some point you have to stop the process and make a distinction between faith and trust. That is, you have to no longer trust that things will go your way-- so as to be able to hang on to simple faith in God that he is One, and he made the world ex nihilo, and he has no reason or obligation to be concerned with you at all. Because at that point, you do not want to lose faith in God because of things getting even worse.
The best solution to this problem is simply not to fail in the original test of faith. To stick with trust in God, even though things are obviously not going the way you want and need. The trouble is that there is no simple formula for how to stand in a test of faith. [I should know..]
Appendix and thoughts.
(1) The arrow of casualty is actually determined by intention. Otherwise it is undetermined.
(2) בטח אל ה' בכל לבך ואל בינתך אל תשען היינו שיהיה לבך שלם במדת הבטחון ואל בינתך אל תשען שלא תאמר אבטח בה' אלא אני מחוייב לעשות ולהשען
גם על שכלי ולכן אמר לא תשען על שכלך אפי' בתורת משענת וסוד העניין שתהפוך לבך לבטוח בה' בכל אז יברך אותך ה' בכל
That is: the Gra also said that reality has to conform to your trust in God.
(3) Just in the way to make it clear what I am saying. If you are in a situation where you are able to learn Torah [That is the Tenach and Two Talmuds], then unlike me, you should not leave. It is hard to find a situation in which one can learn Torah and if one leaves it, it is impossible to return. [By this I do not mean to exclude two topics the Rambam thought were part of the Oral Law, Physics and Metaphysics. It has always been the custom in the Lithuanian yeshiva world to gain expertise on the side, but not during the regular yeshiva session in the morning. However since Physics is hard I recommend the opposite--that is to do the Physics session first thing in the morning and then later the sessions in Tenach (Old Testament) and Gemara.]
(4) Just in the way of explanation: Kant wants to justify universals (synthetic a priori) by means of the fact that reality has to conform to a priori knowledge. This really all started with John Locke and his primary qualities and Descartes. Then it dawned on Kant and even things we consider primary qualities like number quantity and extension depend on the observer.