I think I blogged about this phenomenon years ago already:
In bombing campaigns the more you destroy, the less the enemy has left to lose and the lesser becomes the threat of further destruction while you keep piling up more and more destruction. You can definitely go past some optimum point.
This applies to Russia; the more you punish it for its backyard great power games (such as in the Ukraine), the less it has to lose - and at some point Putin probably decided that there's little else to lose, perceived a huge freedom of action and went into action in Syria.
Well, this or maybe even worse; he may be adding bargaining chips for deals otherwise unrelated to Syria this way!
P.S.: Compare this to my ideas for keeping Putin in check from August 2014 and May 2014, in which I proposed non-exhausting, durable bargaining chips that weren't built on sinking costs.
P.S. 2 : Nobody has ever accused me of writing too little in a too long text. I wonder why..