We don't need to smile when everything is good and perfect, we can smile anywhere and anytime especially when we think we don't need it, because, that's when we actually need it the most...
The Dictionary defines 'Smile'
"As a facial expression comprised by flexing the muscles of both ends of one's mouth while showing the front teeth, without vocalisation, and in humans is a common involuntary or voluntary expression of happiness, pleasure, amusement or anxiety"
I started learning how to smile during my personal workout time especially during my 100 Squats daily challenge !
I observed that it motivated me to pull through and not just that, it filled me with so much joy on the inside.
Usually, when we exercise, we tone the muscles of the body, forgetting the facial muscle by squeezing and frowning which is not supposed to be so..See smiling as a way of flexing the facial muscles and toning them just as you tone the muscles of other parts of the body.
Being a yoga teacher, i like to motivate my students/clients to do those poses they consider difficult by making them smile while in the pose.
Hope you start smiling more these days no matter what happens and even more during your workout sessions!