rocket science 
noun [mass noun, usually with negative] humorous
Something very difficult to understand: we want you to get out and vote—it’s not exactly rocket science...
- Organic weed control is not rocket science, but it does take understanding the anatomy and physiology of the crop plants, the weeds and the soil.
- Setting up on your own isn't rocket science, but it does take nerve and an injection of capital to get you rolling.
- The chord changes aren't rocket science, but the rhythms are fast and the fills are rare, quick and poisonous.