When you're angry at God.
I use to pray, and I even use to go to church faithfully. I was serious about God and Jesus, even joined one of the church ministries and loved it, until "X." In this case, the "X" is whatever situation or circumstance has affected your faith and maybe caused you to doubt whether a relationship with Jesus is even worth it. I could write some flowery words like "God is Good," "God is Able," or a popular one, "God Knows Best," as to why you shouldn't be angry. However, not having experienced the circumstance or situation that has caused the anger would be disrespectful. How do you explain to a person who has experienced tragedy while faithfully serving God that the Lord is still good, loving, caring, and concerned about them? I have often heard people say: "I was steadfast, immoveable, prayed up, fasted, gave my tithes and offerings, worked in the church, and still the Lord did not answer my prayer." I thought God was a loving God; I thought if I did everything according to the Bible, He would answer my prayer. I even quoted from scripture John 12:14, "Most assuredly, I say to you, he who believes in Me, the works that I do he will do also; and greater works than these he will do, because I go to My Father. 13 And whatever you ask in My name, that I will do, that the Father may be glorified in the Son. 14 If you ask anything in My name, I will do it." "Been There, Done That, It Doesn't Work."
I clearly understand how easy it would be for anyone to feel this way when tragedy befalls a loved one or themselves. As this is a tough subject, I dare not profess to have the answer that would adequately address every situation but would like to offer a perspective that most never consider. Imagine you have only one beloved and begotten Son. Imagine if no fault of your Son, people's wickedness required a blood atonement through the form of a perfect sacrifice. Imagine that no grain or animal sacrifice would be sufficient but only that of a perfect lamb of God. Imagine when you realize that the perfect lamb of God is your only begotten Son. Imagine when you know the atonement must come through the form of crucifixion on a cross. Imagine when you have to explain what needs to be done to your Son. Imagine when your Son says, "I'll go." Then imagine your Son in a garden praying not once, not twice, but three times to you, His Father, with the sweat of blood running down asking, if there is any other way. Imagine you hear but not answering. Now imagine watching as your only-begotten Son bears the penalty of mankind.
God and the Lord Jesus, understand. I can't tell you why some prayers are not answered, but if the prayers that Jesus prayed in the Garden of Gethsemane are any indication, there is a much bigger plan than you or I will ever know. So I say "God is God," "God is Able," and "God Knows Best."