Among other things, he invented time sharing:
I'd say he wasn't entirely wrong; he just missed Moore's Law. With cloud storage, apps in the cloud, and apps like Siri (whose brains are in the cloud), personal computers and smart phones are becoming what you could call smart terminals. They can do a lot on their own--personal computers are at the level of supercomputers of yore--and share time on distant, gigantic computing centers.The power of that invention would come to shape Dr. McCarthy’s worldview to such an extent that when the first personal computers emerged with local computing and storage in the 1970s, he belittled them as toys.
Rather, he predicted, wrongly, that in the future everyone would have a relatively simple and inexpensive computer terminal in the home linked to a shared, centralized mainframe and use it as an electronic portal to the worlds of commerce and news and entertainment media.