Do you put conditions on starting new books?

The Glass Rainbow: A Dave Robicheaux Novel - James Lee Burke Saphirblau - Kerstin Gier River Marked - Patricia Briggs Doctor Who: Coming of the Terraphiles HC (Doctor Who (BBC Hardcover)) - Doctor Who and an Unearthly Child - Terrance Dicks

I've been flying through the Mercy Thompson series, but was saving the last one for something and started a long German book recently. I told myself I can't read River Marked until I've finished Saphirblau


I also watched the two Doctor Who specials today, 'The Day of the Doctor' and 'An Adventure in Time and Space'. Now I want to devour my the who books I brought with me even more badly.


But not until I finish the stupendous Audiobook I'm listening to, The Glass Rainbow which is the 18th Dave Robicheaux book, and my first. Amazing on it's own, I look forward to picking up the other audiobooks. 


Please tell me I'm not the only poly-bibliophile who sets preconditions before starting a new book?


So, in the case of the former it's baiting the donkey, in the latter, I can't lose.