Keeping in mind impermanence, suffering and non-self

If one doesn't know the notion of "impermanence, suffering and non-self", can one see it by one's self? I know that I don't need to "force" myself to see impermanence: but do I need to keep in mind "impermanence, suffering and non-self" when practising? EDIT: How much do i need to keep in mind "impermance..", because if it is to low, one can see it but not realise it, if it is to high, one can intellectualize it.