Magic works by bending physical law, allowing an effect to occur that would otherwise be impossible. This is in clear violation of physical law, but the caster has temporarily suppressed that law in their local environment. It is very powerful but very personal.
Technology is the exact opposite.
Technology relies on physical law to operate, and the use of a technological item or skill serves to reinforce the physical law on which it operates. When a technologist shoots a gun, he is relying on the chemical properties of the gunpowder to create a controlled explosion in the gun's chamber and propel the bullet forward. By using this gun repeatedly, he is actually strengthening those chemical properties, making them harder to subvert through magic. Therefore, magic and technology oppose each other. Magic is constantly bending or suppressing physical law, while technology is reinforcing those same laws.