Because an alternative explanation exists that fits the data just as well or better. The way science works is via Bayes Rule: Pr(T[0]|O) = Pr(O|T[0])Pr(T[0])

Because an alternative explanation exists that fits the data just as well or better. The way science works is via Bayes Rule: Pr(T[0]|O) = Pr(O|T[0])Pr(T[0])/sum(Pr(O|T[i:n])Pr(T[i:n])) This tells us the evidence for a given theory given the observations depends on the ratio of two things: 1) How well the observations fit a theory (you can substitute hypothesis/model/etc) and how plausible a theory would be without the observations in question. 2) The above for all other theories In other words, the default for the scientist is to be skeptical of any explanation until the others have been rendered implausible (ie ruled out). There is a bit more to it (eg the Pr(O|T[i]) terms depend on the precision of the predictions, which remain vague in the case of NHEJ despite generous funding), but that is pretty much it.