When the ball drops in Times Square on January 1, 2040, it will still be true that no human will have ever walked on Mars. Elon Musk, if he's still alive, will still be promising to send people there in the next 5ish years. He'll have done a lot of cool things between now and then, but a manned Mars mission will elude him.
People will have finally gone back to the Moon, but there will be no Moon base.
Can you imagine how pessimistic you'd have to be to say, in 1972, that no human would have been back to the Moon by 2020? I tend towards pessimism, but I'd never have said that. Humanity, step up your game.