This is somewhat of a philosophical issue.
Some individuals never delete an image, ever.
No matter how bad they keep it.
It can be argued that the cost of HD space is dropping all the time so why delete images.
Other individuals are ruthless, deleting any image that they do not like often the same day that they shot those images.
I have to say that my personal philosophy is somewhat 'middle of the road'.
Technical errors are deleted early, sometimes in camera but otherwise on import.
Otherwise they are imported, keyworded, and metadata updated.
I come back to images regularly over weeks, months, and sometimes years.
Some images never make the grade and will eventually be deleted.
Any image that I am ambivalent about, I keep.
In general I tend to look at technical issues early on and then later on, once all the technical rubbish has been discarded, I look at the aesthetic issues and so a technically proficient image will be discarded if ultimately it doesn't work aesthetically.
In my photographic journey I recently reviewed all the images I shot in the early days (2007-2009).
I was a little taken aback and disappointed that so many images, 9 out of 10, in fact, did not make the grade - most of them failing on technical grounds like critical focus.
However, as I progressed closer and closer to the present less and less images were binned for technical failure but rather for aesthetic reasons.
I had grown in wisdom though so many the aesthetic 'failures' were in situations where I had shot the same subject in many ways looking for the best composition and light angles so, most of the time anyway, I usually have a good result that is kept.
I fully appreciate that many of the readers of this thread will be 'old salts' to whom none of this is new, however, at least some readers may be in a position that I was a few years ago looking to transition their photography to a new level.
One of the key things in that process is learning to critique one's own work, dare I say it, objectively (or perhaps dispassionately) which is why taking one's time is important to allow any emotional attachment to recently captured images to dissipate.