I often see comments similar to this one. What if the first book is a stand-alone and the second and third (or 10th) are also stand-alones? Would you still say that if #1 isn't picked up none of the others will be either?
No, because agents and editors are humans and operate through weird subjective processes. If the writing and plotting is reasonably solid throughout, you're left with their emotional reactions to your work. All of which can change according to variables outside your control. Book #1 may not strike the right note with anyone during one query round, but book #2 or #3 will get lots of responses. You can't know ahead of time, so don't use that worry as an excuse not to query, either.
This business is crazy enough without writers creating more performance anxiety for themselves.