boggle (one's)/the mind
To thoroughly overwhelm, confuse, or surprise one. The show of support from everyone just boggled my mind. The plot of that move totally boggled my mind—did you understand it?
boggle the mind
Bewilder or astonish with complexity, novelty, or the like, as in The very magnitude of the Milky Way boggles the mind. The source of this usage is unclear, as the verb to boggle has several other seemingly unrelated meanings-to shy away, to hesitate, to bungle. [Second half of 1900s]