Three reasons why the devil was DUMB for this...

1. His death was the actually plan.

Isaiah said, "His grave was assigned with wicked men, yet He was with a rich man in His death, because He had done no violence, nor was there any deceit in His mouth. But the Lord was pleased to crush Him, putting Him to grief; if He would render Himself as a guilt offering, He will see His offspring, He will prolong His days, and the good pleasure of the Lord will prosper in His hand. (Is 53:9-10)

Jesus said that he "did not come to be served, but to serve and give his life as a ransom for many (Mk 10:45)." Peter preached that the death of Christ was "according to God's predetermined plan and foreknowledge (Acts 2:23)". God understood exactly what He was doing. Satan did not.

Dummy move number one was the devil thinking that he could outsmart the all knowing and only wise God (Rom 16:25).

2. His burial was the seed that sprouted the whole Church.

Jesus said, “The hour has come for the Son of Man to be glorified. Truly, truly, I say to you, unless a grain of wheat falls into the earth and dies, it remains alone; but if it dies, it bears much fruit. (John 12:23-24) Jesus's death caused the Kingdom of God to increase in size, not to be eliminated as the devil hoped. The Bible seems to show that God is obsessed with fruit bearing. Bear fruit and multiply is the consistent mission of God's people from Genesis to Revelation and Jesus is clearly stating that His death will lead to the production of "much fruit." And that is exactly what happened.

So dummy move number two was the devil not understanding how seeds work.

3. His death activated the work of the Holy Spirit.

Jesus said "unless I go away, the Advocate will not come to you (John 16:7)." The Holy Spirit's presence inside of every believer acts as a multiplier for the Kingdom of God. This is the opposite of what the devil would have wanted. Instead of dealing with "just Jesus", being limited to time and space in his incarnated form for the 33 years he walked the earth, now we have the Holy Spirit dwelling directly inside of every Christian everywhere. The very name "Christian" means "little Christs". Not in anyway suggesting that we are God as He is God, but that we share His Spirit and His mission. And now, from the inside, the Spirit helps us to be more and more like Jesus, bearing more and more fruit every day (Rom 8:29).

So dummy move number three was not realizing that Jesus death would send the Holy Spirit.