turkish planes were allowed to cross into syrian airspace to bomb Kurds although Russians had the right not to allow them
they certainly didn't think a minor violation of turkish airspace would cause a shooting
mind you it would be totally different if the missile hit the plane while it was in turkish airspace and/or the plane went down there(as I think was the turkish plan), but according to even turkish ministry it was hit in syrian airspace, huge difference
they gave casus belli to Russians now so they can shoot down any turkish plane that just comes near the border and say "you did the same"