Some say that the pessimist is an optimist with experience. And you can understand why. It often happens that one has dreams and projects and after much effort fails. Why, then, should one always trust that things will turn out well?
Besides the “practical experience” of many pessimists, there is —at first glance— even a biblical basis for not trusting that everything will be all right.
In this week’s portion, Shemot,  we read how Moses, adopted by Pharaoh’s daughter, leaves the palace to see how his enslaved brethren are faring. He sees an Egyptian slave-master mercilessly beating an innocent Hebrew slave, intervenes, kills the assailant, and buries him. He believes that there were no witnesses until the next day when he sees two Hebrews fighting with each other and he admonishes them. One of them replies: “Who appointed you as authority and judge over us? Do you want to kill me like you killed the Egyptian?” The Torah tells us that upon hearing this “Moses was afraid and said, ‘The thing is known'” .
There is another historical episode recorded in the Torah where we read about personal fear. When our patriarch Jacob learned that his twin Esau was coming towards him, accompanied by four hundred armed men, the Torah tells us that “Jacob was very afraid” . In that case, the Torah tells us what he did as a result of the fear: “He divided his people and animals into two camps. He said: “If Esau comes and attacks one camp, the second camp will survive.” 
Our sages explain why it was that Jacob was afraid even though G-d had promised to protect him: “My merits were diminished because of all the goodness you did to me, so I fear that since you promised me [protection] I was defiled by sin, which will lead to my falling into the hands of Esau.”
We see from that episode that there are good reasons for not being sure that things will turn out as one would like. It’s not that G-d cannot help; perhaps one is not deserving.
As for the story of Moses, two questions stand out: 1. Why was he afraid and did not trust G-d that nothing would happen to him as a result of his having done something right? 2. Why does the Torah tell us that he was afraid if it does not tell us what he did as a result of that fear (unlike in the story about Jacob)? What purpose does that information serve?
The Rebbe —may his merit protect us— offers the following fascinating explanation, based on the Hasidic adage attributed to the third Rebbe of Chabad, known as the Tzemach Tzedek: Tracht gut, vet zain gut, or “Think well, it will be well”.
“The idea,” explains the Rebbe, “is not that you have to think positively because you have to trust that things will turn out well, but the other way around: things will turn out OK as a result of your thinking positively.
When one trusts in G-d’s help despite the apparent —or real— impossibility of the situation ending well naturally, G-d responds in kind by helping despite the apparent —or real— lack of merit one may have incurred.
This explains why the Torah tells us that Moses was afraid, though it does not tell us what he did about it. In the next verse  it tells us that “Pharaoh heard about it and wanted to kill Moses”. The Rebbe explains that Pharaoh’s reaction was a consequence of Moses’ fear. If he had trusted that everything would go well, there would have been no negative consequences; Pharaoh would not have heard about it and even if he did, it would not have occurred to him to punish Moses. That is why the Torah tells us about Moses’ fear, so that we may understand what led Pharaoh to find out and want to harm Moses.
In short: there may be well-founded rational arguments to justify the fear for the future. There are those who suffer from the so-called impostor syndrome, convinced that they do not deserve the success and fortune that they have. We see that even Jacob himself doubted the results of his possible bellicose encounter with his brother, not because he distrusted G-d’s ability to protect him, but because of his personal lack of merits to deserve such an intervention. Nevertheless, we can and must trust that the results will be tangibly positive, and it is this very trust in G-d that will cause it to be so.
So this week’s tool for dealing with anxiety can be summarized in five words: Tracht gut, vet zain gut.
Based on Likutei Sichos Vol. 36, Shemot (I)
1. Exodus 1:1 – 6:1
2. Ibid, 2:14
3. Genesis 32:8
4. Ibid, 32:10
5. See Rashi on Genesis 32:11
6. Exodus 2:15