Dealing with rejection anxiety as a reviewer
The role of the reviewer is not so much gate-keeper, but rather your role is to help the authors get the paper to a position where it is publishable. So I very rarely recommend outright rejection at the first round.
Once you have written things down what it would take for the paper to be publishable, it maybe the case that this is clearly unachievable and that this author will never get this paper to that level – but that is for the editor and authors to decide.
Reviewers are normally asked to judge two things:

Is the paper sufficiently novel and exciting to be interesting to a large enough fraction of the readership of the journal.

Is the paper sufficiently rigorous to demonstrate the claims it makes.


If the paper is not sufficiently novel or exciting I say:

To make this paper publishable, the authors must explain the additional advances made compared to Smith et al. and Jones et al. and why their work would be of interest to a reader of the Journal of Things, beyond those connected with the sub field of very small things.

Methodological or interpretive flaws I will simply point out and say they must be fixed.
So for example, I recently had to review a paper for a software tool. It unlikely to get published, but instead of saying “reject” I said:


The tool does not appear to implement any new functionality compared to  Jones et al and indeed is missing several of the functions in that tool. The authors should explain why their tool is an advance in comparison, and provide benchmarking data comparing the performance.

The tool was not installable on my system, the authors should ensure that there is a robust installation routine and that it functions on representative range of systems. {goes on to list the problems with the installation}

The tool has several bugs and conceptual errors in it that must be fixed before it was published. {goes on to list them}


In conclusion, the tool has several usability and functional shortcomings that must be fixed. Even if these were fixed, the authors must explain why their tool is superior, or even equal in performance or features to Jones et al.

Now I was 80% sure that this wasn’t going to happen – the amount of work required to bring the paper up to a publishable standard was probably more than had been put into the project up until that point – but if they wanted to do it, I’d be happy to recommend publication. I never saw another revision of the paper – I don’t know if the editor decided to reject it, or the authors decided it wasn’t worth it –, but I fulfilled my role: to say what it was that was necessary to bring it up to standard.
If the authors do decide to try for a resubmission, without fixing the problems I identified, I will just say that:

The authors have not addressed points A, B and C, and I cannot recommend publication until they have done so.


There are several &quot;Peer Reviewer's Oaths&quot; out there. The one I like is from here:
http://www.opiniomics.org/the-reviewers-oath/

I, the reviewer, promise:

to not hide behind a screen of anonymity
to be open and honest with you (the authors) at all times
to be constructive in my criticism
within the rules given to me by the journal, to assist you in every way
I ethically can to get your manuscript published, by providing
criticism and praise that is valid and relevant