Why is an olefin inert to nucleophiles?
Because the alkene, the olefin, is an electron-rich species,
You can bubble ethylene thru an aqueous solution of water, and ethanol, containing potential nucleophiles such as cyanide, or halide, or water or ethanol themselves. The ethylene is inert to these nucleophiles, these electron rich species.
Add a bit of acid, i.e.