For anyone else, it is much tougher. It is even worse to not belong to an institution at all and to write from a home address. It is also a disadvantage to be unknown in the field, to have no prior publications, to be female, to be too young or too old, or to be from a country with low scientific status. Although the rhetoric about science is that ideas count, not who expresses them, in practice ideas are commonly judged by their source. Ideas are given much more credibility if they come from a respectable source.
Outsiders face an uphill battle.
Just as important is presenting one s ideas in the expected way. A paper, to be recognized as scientific, must conform to the standard mold. This mold varies from field to field, but usually means a restrained, impersonal style, suitable references to earlier work, and use of jargon appropriate to the topic, all in a concise package that is similar to other writings in the field. Anyone who writes about their own personal discovery, not mentioning prior work, and writes for a general audience, has little chance of being published in a scientific journal, even if the ideas are conventional and would be publishable if they were in standard form. Once again, rhetoric about science might suggest that contributions should be judged on their content rather than on their appearance, but the reality of the situation is otherwise.