Bayesian statistics is sometimes called subjectivist statistics. Probability in Bayesian statistics reflects your degree of belief in some potential outcome.
If you conduct an experiment, you use Bayes’ theorem to update your degree of belief, which is now conditional on the outcome of your experiment.
By quantifying your degree of belief in a prior, you give yourself some starting point (rather than just assuming 0 probability), even if that prior is only an educated guess and not some well researched position. This can be good because you might not have done the research yet.
If you conduct an experiment, you use Bayes’ theorem to update your degree of belief, which is now conditional on the outcome of your experiment.
By quantifying your degree of belief in a prior, you give yourself some starting point (rather than just assuming 0 probability), even if that prior is only an educated guess and not some well researched position. This can be good because you might not have done the research yet.