Neither human brains nor contemporary computer systems "think" functionally. There will always be an impedance mismatch between the way we naturally frame operations and functional logic.

In my mind, this means we'll never see pure functional programming dominate the software creation world. I think we will continue to see aspects of pure functional programming trickle over into otherwise-imperative languages, but frankly the way parallelism is going I think we'll end up writing most software in a hybrid declarative-imperative model in the mid-term future.