Impermanence (Anicca) and Mindfulness in general

1. Did the Buddha meant to be attentive all the time or is that just an ideal to strive for? 2. If we are attentive and feel sensations do we always see the impermanence in them? So first to recognize what is going on in- or outside and then seeing the impermanence and potentially the unsatisfactoriness in them, right? But wouldn't that decrease pleasures in certain activities/objects?