The Fence sits 200 meters inside Israel. There are markers 200 meters inside the fence on the Gaza side indicating where the border with Israel is. Once a Gazan crosses the 200 meter mark they are in Israeli territory. They all know this. They are playing a game of political chicken. If you cross the border without permission of most sovereign nations in this world you are at risk of being shot. Before firing Israeli soldiiers are required to warn those already in Israeli territory that they have illegally crossed the border. Refusing the warning to return to the Gazan side of the border is likely to gt you shot for illegally crossing the border. There is no reason for a Gazan to cross into the buffer zone except to create a situation between Israel and Gaza. Stay outside of Israeli territory and you won't be shot for crossing the border illegally. Simple.
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from the article: Israeli troops shoot Palestinian approaching Gaza fence