Oh no, the memories.
I was sending a nice fancy lander to the Mun once. It was a well tested, decent design, and iirc this was the seventh time I had used it. I EVA'd the Kerbal on board to do a check of the outside of the craft (I wanted to practice my jetpack skills.) After a visual inspection, everything A-OK. I went to re-enter the craft, when I realized that the hatch was pointing down. I tried everything, different angles, speeds, even pushing the ship. Nothing worked. Finally, the poor guy ran out of fuel, and I had to leave him drifting in orbit around the Mun.
This was, of course, before I knew anything about rendezvous, or that you could just click and drag the Kerbal to change his orientation. After I found those things out, his loss became even worse.
From then on, each of my lander designs was equipped with an auxiliary probe core, just in case.