Classic KSP. An hour into a mission and you realize you never added batteries and you can't move your probe because the sun isn't hitting the solar panels. Or

Classic KSP. An hour into a mission and you realize you never added batteries and you can't move your probe because the sun isn't hitting the solar panels. Or even worse, you realize as your crew is barreling towards Kerbin that you forgot to add parachutes to your lander...