One of the worst trials of our faith as Christians can be an illness or injury or attack that we didn't expect. Some of us "passively" don't expect such things to happen to us, meaning our minds were not on the subject and we just didn't devote much thought to it. We just weren't expecting the person behind us, (in a Ford F250 pickup truck, no less), to keep moving when we braked for a yellow light to avoid going through the red light. We just weren't expecting that mole on our back to become malignant, or to have a workplace injury and find out we had torn ligaments. Then again, especially if we are fond of the so-called "Prosperity Gospel," we may have an "active" expectation that God will not let such things happen to a believer "in good standing." We may conclude - more or less judgmentally - that if He did allow it the person is out of favor with Him due to some sin about which he or she hasn't told us. (Job's "friends" are the classic example in Scripture of that.) We may simply have been expecting that God would not let whatever happened take place at all.
What we "expect" of God has its roots in what we call "faith." Saving faith is not placing our trust in what we know about God, or think we know. It is not even placing our trust in what we know of God's Word. Saving faith, (subject to Biblical definitions such as Ephesians 2:8,9 and Hebrews 11:1), is placing our trust in the nature and character of God as a Being who exists. "But without faith it is impossible to please Him; for he that cometh to God must believe that He is, and that He is a rewarder of those who diligently seek Him." (Hebrews 11:6).
Are God's promises something we should trust? Yes, as long as we recognize that there can be a difference between what God has actually promised and what we think He has promised. This may be a matter of misunderstanding whether a promise that God did make in Scripture applies to us, or misunderstanding what He said He promised. Sometimes we may have inferred a promise where God didn't actually make one. Lawyers study in law school how to write contracts because people tend to infer promises and guarantees where none were made, some out of honest misunderstanding and some out of utter chutzpah. People do the same things to God. The greater our misunderstanding or mistaken inference, the greater will be our disappointment, perhaps even our anger, when God doesn't meet the expectation we formed.
There is a difference between trusting in God and in a mental picture of God or in what we believe we can expect of Him. This is one of the chief reasons, though not the only one, why God allows misfortune in our lives, (see Hebrews 12:9-11), to correct us. He wants to correct our misunderstandings. He wants us to see that the patterns of thought we have constructed don't allow for some things, and to seek better answers from Him.
If our trust is the kind of trust Job had, ("though He slay me, yet will I trust Him"), or that Paul had, ("For the which cause I also suffer these things: nevertheless I am not ashamed: for I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day," 2 Tim 1:12), we may have to confess the inadequacy or inaccuracy of our expectations, and we may have to alter what we expect of God, but we will not stop trusting Him or lash out at Him because He didn't meet our expectation.
God is not always interested in meeting our expectations. He wants to meet with us.
(See "About Me")