Doubt is not so much a sin as it is a problem, and like most problems, it’s best to solve it, as opposed to letting it be a part of our continued existence.
Too often, when a Christian asks a question about God’s goodness, or His ability, or His trustworthiness, the response from others in the room is one of alarm and chastisement: “Trust in the Lord always! He is good! Amen and amen! Praise Jesus!” And . . . end of conversation.
Whatever provoked or caused the doubt in that person’s heart hasn’t been addressed, and all we’ve really gotten across is that you, as usual, don’t believe the way you’re supposed to; you, as usual, are at fault for your lack of belief; and you, as usual, should just keep quiet and pretend you have no problems.
Just like the rest of the people in the room are doing.