Day 14: A question for the ages

Why do spiders insist upon building their webs across the paths where I walk?  (These are big spiders, but I honestly don't think they have any hope of catching a human.)

Also, why do they keep building their webs when things (read: me) walk through those webs and break them? (Please note: I don't do this on purpose.  I don't do this on purpose for two reasons, actually: one, it would be mean; two, I might end up with a spider in my hair.)

Does this mean that the kinds of things that spiders actually hope to catch and eat are flying along the same paths where I walk? 

I imagine that this must be frustrating for the spiders.  I can see the blog post now:

Weaving Spider
Day 14:  WTF?
Why do humans persist in walking into my web every morning??  I just finish getting the darned thing woven, and I settle down for a nice rest before the gnats start flying around, and bam!  Human!  You'd think they'd learn!