Swimming upstream means lot of effort, which sometimes we do not have.

Secondly, the natural state of things is to minimize the entropy. We need predictability, and the most usual situation when the water level goes down, is to swim downstream. To have an intelligent decision, we need the information to differentiate between that dangerous situation (the dam that is built to take control over our lives) from the many natural situations in which the water just runs in the stream. This is the hard one! And no one has other solution to this, other than experience and education.