Do you know this? “We’ve already put 80 hours into it, we can’t stop now even if the reasons and expectations for why we’re doing something have changed!”
Yes, you can. And you should.
Otherwise, we create a logic where past investment justifies future loss. If we say yes to something, we have to say no to something else. If we try at all costs to finish a project that no longer makes sense to the customer, we can’t work on something that can benefit them in the future.
The most expensive thing is not to let go of something we’ve invested in. The most expensive thing is to finish something that no longer has value.