joshi tm: I think when you are the doubling player the opponent could always redouble when he thinks he is winning, so if you double there allways will be 4 point at stake when you double on turn 1.

I doubled because my rating is 1746 while Herlock Sholmes rating is 1560. If those ratings are our true strengths, the expected score is 0.74 - 0.26. Who wouldn't double in backgammon if the their equity was 0.74?

Of course, ratings only approximate true strength, but given enough games, it's a fair estimate.

And if my opponent waits to redouble when the position gives him a winning advantage - I would resign, losing 2 points, not 4.