The first movement of surya namaskara is an absolute positive movement. At first I stand tall and then I take the arms up to the sky. I look upwards to my thumbs or to the sky to check if there are clouds or sunshine. Doing this first movement it is almost impossible to be sad, disappointed, shy, timid or whatever.
That's why it might be so difficult sometimes to start. The very first movement evokes a change of thinking - from looking down to looking up, from passive to active.