The construction here has to do with a word like "doubt." To doubt, there must be something specific to doubt. Don't use wishy-washy words like "whether" and "if." Not, "I doubt whether our team will win today," but, "I doubt that our team will win today." Contrast the following: "I wonder whether our team will win today." Further, be careful how you doubt. Recently a college baseball player, after an amazing win of marathon length, exclaimed, "We never doubted we wouldn't win the game." Sorry, but that statement means they were sure they wouldn't win. He should have said, "We never doubted we'd win the game."
A common mistake similar to the last one mentioned involves the construction, "I could care less." That statement indicates that I care some and could lessen the amount I care if I choose. To indicate that I care virtually none at all, I should say, "I couldn't care less." In other words, it would be impossible for me to have a less caring attitude. That's exactly what I'm trying to say.