Could someone elaborate on how accurate the results of these simulations are generally considered to be by the broader scientific community? It seems to me that

Could someone elaborate on how accurate the results of these simulations are generally considered to be by the broader scientific community? It seems to me that the universe is so insanely complex that any simulations we can currently make would be fairly inaccurate because of lack of knowledge. Couldn't that cause a problem of building a whole base of theory on unproven guesses? I guess the researchers all know that but I'm just curious what the actual attitude towards this kind of work is.