Common sense is used so often because, as you said in many circumstances that is the only knoledge we posses on the subject or that is just the first knowledge that we think of. And to answer your other question, no. common sense is never your only way of knowing. In every circumstance immaginable from cleaning dishes to advanced physics you are always able to re think your basic instinct/knowledge. no matter what, humans have the abbility to go back over how they came to a conclusion and decide if that was the appropriate coarse of action. that is the diffrence between humans and animals while we are able to think through situations animals must relie on their instincs to live.
p.s. i have trouble with spelling