Lack of Visible Alternatives Used as Evidence for Purely-Speculative Explanations

Just a quick note that purely-speculative explanations are often justified by an appeal to the lack of alternative explanations. (Sometimes this is in the form of Dawkin's "Appeal to Personal Incredulity".) The problem with this is that it assumes you have complete knowledge and understanding of possible explanations, which is pretty impossible for us finite beings who can't see the future. If you look at history, you can see both how common, and invariably wrong, such claims are.