Reason can be used only when looking critically back.
Moreover, in the experimental sciences, the scientific fraternity must test a new theory to destruction, if possible.
Meanwhile, the originator of a theory may have a very lonely time, especially if his colleagues find his views of nature unfamiliar, and difficult to appreciate.
The final outcome cannot be known, either to the originator of a new theory, or to his colleagues and critics, who are bent on falsifying it. Thus, the scientific innovator may feel all the more lonely and uncertain.