You are not, in my opinion, a sap.

You are a person that saw somthing wrong in the world (liter), who could
quite easily do something about it, and did it.

I think the reason people do things like this is because their sense of self
only extendes to about the edges of their skin. I don't like to say that
such a person is "selfish" because I believe in self interest as a positive
force.

In my view it was your healthy self interest that made you pick that plastic
up. I would pick it up because I have a sense of self that extends to
others. To seeing that it's important for me that others are not needlessly
hurt, etc.

I can't say that I never do something wrong like liter. But I almost always
try to pick up more than my share whether I'm out in the boat or walking
down the road. The same type of behavior goes for me in other areas like
tipping at restaurants, being nice to other dirves on the road even when
they are jerks, being kind by letting people go ahead of me in the
supermarket line if they have few items, etc.

Once in a while I notice that *I've* done something wrong. Maybe I realize
that I tipped less because I calculated wrong. Or maybe I'm in a big hurry
or a bad mood or just not thinking and I do something I really normally
wouldn't. Of course the person I
*did* whatever to doesn't know it. But I'm comforted knowing that I'm not
usually like that. I realize that we're all human and
sometimes make mistakes.

Another thing to consider. Sometimes something happened that you don't know
about. Maybe that guy put the plastic in his truck but it blew out (or
something like that) and for whatever reason he didn't notice. Sloppy, yes.
But I try to remember that sometimes other do bad things by "mistake" just
as I do.

As for being a sap. My American Heritage defines it as, "Slang. A gullible
person; a dupe."

I can see how picking up after another person might make you feel that you
are doing all the work for someone else's fun. But was it really that hard?
Doesn't it give you some satisfaction to have done what, at least in your
mind, was the right thing? You (and I) don't do these things to help the
slob that left it there. We do it for ourselves and for the other good
people
we respect in the world.