What is the onus probandi rule?

Could you please clarify the meaning and significance of the onus probandi rule? It seems to be a fundamental principle in legal proceedings, but I'm not entirely sure how it applies to various cases. Could you elaborate on its origins, purpose, and potential consequences for those involved in a legal dispute? Additionally, how does the onus probandi rule intersect with cryptocurrency and finance, if at all? I'm eager to understand the intricacies of this rule and its potential implications in the realm of digital currencies and financial transactions.