dwelling on past and future also happens -------only in the present moment----in fact, the whole life , eating, breathing, working, playing, singing, thinking, all aspects of living happen only in the present moment

what ever we may be doing, all moment by moment , happens in the present moment 

what exists is only the present moment , past is gone, future not come 

if so ,then , why to try and struggle to aspire for living in the present moment ----not at all necessary, 

we are in fact, living in the present moment, whole life , moment to moment