"Arise therefore, and get thee down, and go with them, doubting nothing: for I have sent them." (Acts 10:20)
You can understand with so pivotal and important an advent as the birth of Christ, how Joseph would need an angelic visitation to put his mind at ease. Also, it happened in a dream. The angel visited Mary in broad daylight. These agents (or one; could've been Gabriel in both cases) of extra-dimensionality show up in all their resplendent glory and by their very presence--as well as the memory of them--allay any doubt as to what should happen. Because when you're dealing with humans and their choices, we tend to need something higher to help us along the way to God's perfect will. Jesus asks Peter why He doubted as He "stretched forth His hand, and caught him" (Matthew 14:31). The proof, in that case, was in keeping one's eyes on Christ as the worst swirls around you trying to get you to let slip your anchor in Him. Words like faith and hope must necessarily be verbs and not just nouns (more than gerunds, too). These concepts must be planted in our mind while their roots make their way into our heart.
"Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of His counsel, confirmed it by an oath: That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us: Which hope we have as an anchor of the soul, both sure and stedfast, and which entereth into that within the veil." (Hebrews 6:17-19)
And here's where the memory part comes in. It says plainly in the above passage that "it was impossible for God to lie". Paul writes to Titus (1:2) "God, that cannot lie". The same line of thinking goes along with Jesus' equation of Himself to the chief corner stone. He says "Whosoever shall fall upon that stone shall be broken" (Luke 20:18) See, if we really want to know God, we must see this unbreakable aspect to His character. Impossibly hard. The unstoppable force in the immovable object and transcendent to all comparison. God cannot lie. But we can. Amazing. Remember the things God has shown you. Choose to believe that He's telling you the truth. And that it is Him showing you. He won't lead you astray.
What has God shown you and told you? I would say it starts in His word but then He speaks in other ways, too. He speaks through our desires. Through voices we don't have access to. Through impressions and urges and notions. His voice might carry quietly on the wind and be nigh imperceptible but He cannot lie. His words to you and for you are as solid as He. Don't doubt. Better yet, let the wind that brought the word, carry the doubt along with it. Sometimes, we can't help but doubt. Not just what God may be doing in a particular area or instance, but Him too. "Doubt" has its root in "two", just so you know.
"I will worship toward Thy holy temple, and praise Thy name for Thy lovingkindness and for Thy truth: for Thou hast magnified thy word above all Thy name. In the day when I cried Thou answeredst me, and strengthenedst me with strength in my soul." (Psalm 138:2-3)
Real quick and this is just semantics but if it says God "magnified [His] word above all [His] name", and His name is a word, what does this mean? Seen this way, I suppose the answer would apply to Jesus as the Living Word. It really is this simple--at least to God. He's holding a place for us and He sees the reality of all His promises as applied to us. But doubt will stop things up. Doubt will keep us from receiving the things He has for us. In the top verse, the Holy Spirit Himself tells Peter to remain strong and believing. Sometimes, that's all we can do. Keep believing, hoping and loving on God. His faith in you will burn through the doubt and *gasp* you'll be made stronger through it all. And now you can lend that same confidence to everyone the Holy Spirit has you encounter.