halacha - Is the mitzva of 'Shikcha' the act of forgetting, or the act of not going back to collect what was forgotten?

Someone asked me a riddle: what mitzva can be done without kavana? Answer: Shikcha.

I contended that the mitzva is the act of seeing what was forgotten and not going back to collect it, therefore it is done with kavana.

Do you have any proof either way?

Would the act of forgetting fall under the categor of 'misasek' (edit - maybe misasek is not the correct term? I was taught that if you are walking indoors and by mistake your body or clothing flips a light switch, there is no sin, and this is called misasek. Your main action was walking, an unintended 'side action' was flipping the switch. That's what I was referring to - here also, your main action is to collect the wheat, the unintended act of forgetting would be considered misasek, if what I've been taught is true)? Actions that are considered 'misasek' are normally not attributed to the one who did them. Perhaps this is proof that the mitzva is the act of not going back, for if it were the act of forgetting it would be misasek and there would be no kiyum mitzva.