Horror stories: You also asked the following question:

Are there any horror stories of waiting several months after a reviewer agrees to look at your paper, only to get a rejection letter?

First, time between submission and acceptance might look something like this:

• administrative screen (1 week)
• editorial screen with potential for desk reject (1 to 4 weeks)
• potential reviewers are contacted
• time for reviewers to complete assignment vary and review process is determined by slowest reviewer (can be anything, but often 1 to 4 months)
• editor/action editor has to review external reviewers (anything from days to months) and reach a first-round decision.

As an author, you don't usually find out how long the components of the review process take. Your question implies that there is one person "a reviewer" deciding to review and then rejecting. But rather, these are usually different people, and there are multiple reviewers. At most journals, the external reviewers inform and make recommendations to an editor / action editor. They do not make the decision.

So in general, there are different norms about how long a review takes. But in my field of psychology (1 month is amazing, 2 months is nice, 3 months is par, 4 months is okay, 5-6 months is slow, beyond 6 months would be concerning). Other fields and journals have different norms. The point is I would not see waiting 4 to 6 months as a horror story. It's a bit slow. But It's just how long things sometimes take, and something that might factor into where I send my work in the future. And the length of time has almost nothing to do with the outcome. So in general, rejection is unpleasant and slow review processes are also unpleasant, but they're separate issues.

If the first-round review process is taking an amount of time well beyond the norms of your discipline, then you may wish to contact the journal to see what is the hold-up. Based on the response you get, you could weigh up the pros and cons of withdrawing your manuscript. That said, given the energy that may have already been invested in reviewing manuscript, I'd see withdrawing a manuscript as very much a last resort.

My own experience broadly in psychology would go like this:

Desk reject: This is where the article does not get sent out for external review. Rather someone on the editorial team (e.g., editor, action editor, a team) review the manuscript and deem that it is not worth sending out for review. Desk rejects are usually quite quick (e.g., 1 to 4 weeks is common in my experience). Note that not all journals do desk rejects, and many journals vary in how much they filter at this stage.

First round rejections: This is where the paper is rejected after the first round of external review. In my experience, the time to reach a decision is often unrelated to the outcome, and therefore it takes as long as the review process takes. Your question implies that a reviewer looks at a paper and can quickly determine that it should be rejected. It's more likely that the manuscript is sitting in a reviewers inbox, and the reviewer is waiting to find the half-day or so to review the paper. In my area 2 to 4 months for an external review is common. But as you'll read, first round review times vary a lot between journals and fields, and from manuscript to manuscript.

That said, occasionally I've had review assignments taken away from me around the one month mark because one of the other reviewers gave a review sufficient to make it clear that the paper should be rejected. And sometimes editors will get an additional reviewer, if the first set of reviewers are inconclusive. So occasionally, the external review process may be quicker if it's a clear reject. But in general, the length of the first round review process is not diagnostic as to whether it will be accepted or rejected.

Second/third/etc round rejections: Your question does not seem to be asking about rejections at this stage. But the general point remains that the time to get a response is relatively unrelated to the outcome. Perhaps the main question here related to time wasting is where the journal gives you a revise and resubmit but then rejects your manuscript after you make the revisions. In general, good journals will give you a sense of what the likely outcome is if you conscientiously make the revisions. Some will use language like accept subject to revisions, minor revisions, major revisions, allowed to submit again, etc. This can give you some sense of the scale of revisions. Sometimes the editor will say that you can resubmit, but that it is a "high-risk resubmission". Thus, good journals will manage expectations about what the likely outcome will be given a thorough and conscientious implementation of the requested revisions.

Short Answer: Desk rejects are quick, but if it goes out to review, then rejections tend to take as long as any other first-round outcome. So if you haven't heard anything from a journal after 2 or more months, it probably means that your article has been sent out for review, but nothing more.

Longer Answer

Desk reject: This is where the article does not get sent out for external review. Rather someone on the editorial team (e.g., editor, action editor, a team) review the manuscript and deem that it is not worth sending out for review. Desk rejects are usually quite quick (e.g., 1 to 4 weeks is common in my experience). Note that not all journals do desk rejects, and many journals vary in how much they filter at this stage.

First round rejections: This is where the paper is rejected after the first round of external review. In my experience, the time to reach a decision is often unrelated to the outcome, and therefore it takes as long as the review process takes. Your question implies that a reviewer looks at a paper and can quickly determine that it should be rejected. It's more likely that the manuscript is sitting in a reviewers inbox, and the reviewer is waiting to find the half-day or so to review the paper. In my area 2 to 4 months for an external review is common. But as you'll read, first round review times vary a lot between journals and fields, and from manuscript to manuscript.

That said, occasionally I've had review assignments taken away from me around the one month mark because one of the other reviewers gave a review sufficient to make it clear that the paper should be rejected. And sometimes editors will get an additional reviewer, if the first set of reviewers are inconclusive. So occasionally, the external review process may be quicker if it's a clear reject. But in general, the length of the first round review process is not diagnostic as to whether it will be accepted or rejected.

Second/third/etc round rejections: Your question does not seem to be asking about rejections at this stage. But the general point remains that the time to get a response is relatively unrelated to the outcome. Perhaps the main question here related to time wasting is where the journal gives you a revise and resubmit but then rejects your manuscript after you make the revisions. In general, good journals will give you a sense of what the likely outcome is if you conscientiously make the revisions. Some will use language like accept subject to revisions, minor revisions, major revisions, allowed to submit again, etc. This can give you some sense of the scale of revisions. Sometimes the editor will say that you can resubmit, but that it is a "high-risk resubmission". Thus, good journals will manage expectations about what the likely outcome will be given a thorough and conscientious implementation of the requested revisions.