It's better to ask forgiveness than permission
It's better to ask forgiveness than permission is a phrase normally expressed as a truism.
When seeking to do something that between a self-evidence yes and a self-evident no, this axiom present the authority figure in charge will lean to saying no on ground that less could go wrong that way. However if presented with fait accompli the issue will be not a big enough deal that any blowback will be minimal and easier to deal with convince them to change the presumptive no to yes if asked before hand. Based on forgiveness is enviable if any problems caused is not worth ending the assation over.