In the end of the day, humans are like this. If faced with the option of saving oneself or another person, most people would choose themselves (unless it's a parent/child situation). In fact, in most jurisdictions, it's not a crime killing in this circustance, but a self-preservation act that nulls any penalty.
In the case of the Israel/Hamas war, Isreal will think of their citizens first and Gaza's citizen's last. And let's not fool ourselves: the Gazan population elected the Hamas with more than 60% of votes. I bet the IDF soldiers think of that before showing excessive pity towards the Gazan population.