[Sloth]

The one clear fact is that whoever votes third party benefits the opponent of that person's second choice. Thus, if you would have voted for a conservative over a Democrat, but voted third party, you helped the Democrat, and vice versa.

How? You say it's a "clear fact" but how did I help ANYONE except the person I voted for?

[SKempis]

It is right there - could not be more simple. Unless the 3rd party is a serious threat to the Dem, if you would have given your vote to the conservative, but did not, and instead took that vote and gave it to a third party, you helped the Democrat by giving him one less vote he must match against his real threat.

Now, instead of your conservative vote cancelling Joe Blow's Dem vote, making the balance equal (con=+1, Dem=+1), Joe Blow's vote gives the dem advantage (con=0 Dem=+1), whatever the final outcome.