Burning Bridges

Ever wonder where/when the term 'burning bridges' came about? Clearly the term is suitable, but why not 'don't expect to be friends/foster relations with an enemy that you had formerly beheaded and thereafter placed said head on a stake to scare others away'? Or 'don't give someone the HIV or the H1N1', or even, 'bastardizing ones' kin'?? Cruel, yet all with the same overall effect of ostracizing oneself for gain at a solatary point in time and after that gain is achieved, effectively 'burning bridges' when the individuals recognize you actually had alterior motives. Sometimes it's an honest mistake, albeit honest or not, a mistake. Other times it's intentional and only satisfying for a small point in time until you realize that that mistake will ultimately have consequences... To burn the bridge or not??