Yes, we choose to be ‘alive’ (in a sort of a way) to some perceptions but we let it die on us and quickly make it---and ourselves---the past. We note the perception. We label the perception. We react to the perception (in the form of, say, attachment or aversion) on the basis of, among other things, mental images, memories, opinions, beliefs, judgments, prejudices, preferences, evaluations, as well as so-called knowledge and conditioning---and we interpret the perception. Instead of just 'seeing' or 'observing' in a direct, immediate and spontaneous manner, we subject the otherwise fleeting perception to the whole content of our consciousness stream. And, not only that, we start to analyse and judge it---thinking, thinking, thinking. There is no end to it. And where there is thought, there is no awareness. None.
The result---analysis paralysis, judgment, all rooted in the past. For varying lengths of time we cease to be present in the now---we’re stuck in the past. And that's not a good place to be.