There is a strong trend or pressure or theme in our society about having a positive attitude. You read about people who feel that they beat cancer by thinking positive or visualized their way to great wealth and happiness or whatever. I am not going to opine about whether those stories are true or not, but I am going to say that it is not all that important to have a positive attitude during a workout.
Workouts are challenging. They’re supposed to be. We are, on purpose, pushing our bodies to do more than they’d choose to do on their own (bodies are really really good at finding the easiest way to do something). We do not need to project our inner ballerina while we work out; we are not performing for an audience. It is all right to sweat and swear and whine about how hard things are. Smiles are not essential to the process. We do not have to put pressure on ourselves to do the hard thing and project enjoyment the whole time—workouts are for bodies, not for character development.
That said, it is definitely all right to celebrate that record lift or new fastest time. It is all right to make silly jokes and to take ourselves lightly while we lift heavy.
The important bit in all of it is that we show up and do the work.