I have submitted one of my work in a good journal (impact factor 6) and I got rejection after a few weeks. Though I was pretty sure that I covered all the experiments or stuff they can ask for. The reply mail did not show any cause. They just regretted that they cant publish my work. What can be some reasons behind this?
It would depend on the field obviously but I'll have a go at the most common I see in my area.
- Outside the scope of the journal
- Has been done before
- Incremental - minor value
- Value of the work was not clear
- Not appropriately supported with experimental results
- Badly presented in the context of the discipline
- Badly written
At good journals, publication is a competitive process.
They get far more acceptable papers than they can process, so it's not true that all papers that are good enough are accepted. Only papers that are better than almost all the other papers that are submitted are accepted.
If your paper did not go out for review, it's likely that, even if the paper was done as well as a paper with your particular results could be done, it still wouldn't have been accepted, because the results are simply not interesting enough compared with the results in other submitted papers.
It should "go without saying", but apparently does not, that you should have advice from experienced people/faculty both prior to submission, and after receiving reviews. That is, an essay which might seem reasonable to a novice (we have to admit that, at the beginning, we are indeed beginners) is (potentially) viewed as too rough and naive to more experienced people.
This is why you need advice before submitting, to be sure you're "in the right ball-park" (meaning "approximately ok").
There are many other random factors in play, of course. And some of these can be randomly fatal. Ok. But the main non-random feature you yourself have some control over is the style, tone, etc., of the document you send.