We've all been there. While Kerbals like to sneak onto our rockets solar panels apparently like to vanish once in space (you added them, you KNOW it!). Kerbals make due without ladders, SAS, or sometimes without fellow Kerbal contact for years while they wait for the rescue mission you swear you'll get to someday. So, as the title asks, what is your biggest blunder in KSP? I made mine recently. I had launched a moon lander/orbiter paired ship and made it to Munar orbit after a lot of tweaking and time (I'm still relatively new to the game) and undocked the lander from the "mother ship" that had enough fuel in it for me to knock out all of the biomes on the Mun. I had placed a nose cone on a decoupler on the engine of the lander as it was upside down and on the top of the rocket at launch. In Mun orbit while controlling the lander I hit the space bar, the decoupler fires and nothing happens.... I had attached the nose cone directly to the engine some how O_o. Had to redo all my work. May not seem like much to you experts but it was a very costly error for me. So I'm excited to hear about your greatest "oh duh" moments!! Cheers!