Hypotheses supported by multiple tests are stronger. A scientific theory is a set of related hypotheses that, taken together, form a broad-ranging, testable explanation about some fundamental aspect or phenomenon of the natural world. But, relative certainty is sometimes very impressive. Many theories withstand vigorous, extensive testing. They may be added to or modified but are not likely to be disproved.
Scientists are people Scientists strive to discover objective explanations about the real world.
However, they are human, like mechanics, farmers and stockbrokers, and they are thus subject to personal biases, ego and politics. Science is imbedded in the culture, society and philosophies in which it develops. Available technologies and worldviews often limit and direct the questions that scientists ask. For example, no one could ask questions about the effects of radioactivity on genes before the concept of inheritance via genes developed. Nevertheless, ideas are constantly tested and so science is always changing, more closely approaching accurate explanations of nature.