"For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it?" (Luke 14:28)
In other words, it's not wise to get involved in a project--really, regardless of scope and size--without first thinking it through. Jesus condemns the willy-nilly initiation of such. Because if you don't know how to keep the enemy out, it's not worth building above ground. And again, Jesus speaks of our life as either built upon the "rock" (Him) or the "sand" (Matthew 7:24). The storms will come, this is guaranteed. But remaining in Him through them will ensure you're still standing when they go.
"But unto you I say, and unto the rest in Thyatira, as many as have not this doctrine, and which have not known the depths of Satan, as they speak; I will put upon you none other burden. But that which ye have already hold fast till I come." (Revelation 2:24-25)
Jesus speaks of the devil here in ways that make me shudder. It isn't because I forget he's been soundly defeated by Christ's death and resurrection. And it isn't because I'm not sure of my standing as a believer. It's something subtler, deeper. The deeper you get with God, the more you are expected to live out what you know. Life isn't about skating by on surface perception. It never is, but with the Lord, as He always wants to take you deeper, He'll begin to teach you how the other side operates so as to keep the devil out. Out from the inevitable attempt at reentry in order to try and screw up what God's doing. Think about a dream. You awake from sleep and maybe you feel weird and you don't know why (this happens to me a lot). But the reason upon reflection is that dream that didn't make sense. Maybe it held some instance that doesn't sit well or wouldn't be good if real. It's like this with the devil. He's there at the beginning of what God's doing, trying to insert a negative in order to make the whole thing eventually crumble.
"Lest Satan should get an advantage of us: for we are not ignorant of his devices." (2 Corinthians 2:11)
It doesn't have to be anything earthshaking. Paul, above, speaks of the forgiveness of an offense. It could be something as simple as believing an innocuous-seeming lie. This is why we need the Holy Spirit. Ignorance of the grace is no excuse. As the Holy Spirit sees every little thing that we meet in our thoughts (and dreams), He'll be sure and either keep out the bad stuff or at least reveal it so that we might pray on it and as such, bypass it. God wants to see your dreams come true and come to pass. He'll make sure of it.
"Put on the whole armor of God, that ye may be able to stand against the wiles of the devil." (Ephesians 6:11)