Taking time to celebrate is not a rejection of the work to come. Throwing cold water on everyone not even 24h after winning is like a boss reminding their employee to be on time the next day, at the employee's birthday party.

You can celebrate. You can take a sigh of relief. And also, there is more work to come after that.

ETA: taking time to celebrate is a ritual practice that galvanizes the moment and marks these important moments in our psyches. Refusing to do so is missing out on a wonderful and powerful biological mechanism humans possess.