A Question in my Mind

In this fast paced world, with technology wearing a new suit every day , we meet so many people and see so many new things. But why is it that, certain people/things have such an impact on us, that though they/it has passed us, we still remember it or rather keep thinking about it..... It is not ours, it is just something that came across us, but once it has gone past us, why is there a feeling of losing, why are we not able to understand that it was not ours and it would never be ours....why is it that we fail to respond and instead react to such situations....i donno, i just can't find an answer for all these questions........