A Mystery: Why Can't We Walk Straight?

Maybe it's asking the wrong question.

Why can we walk straight? It's not an easy thing. Think about it, can you draw a perfectly straight line? It's really hard.

We can walk straight because we can see the target and adjust our movement all the time. If we can't see the target, and we have nothing to measure to, we can't adjust our movement.

I wonder if most humans can crawl straight?

tl; dr;

there is no answer