I have an Adafruit Micro SD Breakout Board attached to an Arduino MEGA2560. Running CardInfo I couldn't get the card to initialize. I triple checked the wiring, tried a few different cards, nothing. Eventually through jiggling all the wires and poking at it in hopes I could find the issue I discovered that if I pressed my thumb against the back of the card slot (as shown in included picture) it would initialize the card perfectly. After I take my thumb off it will continue to recognize the card each time I hit the reset button, as long as I hit it every few seconds. If I wait longer than ~10 seconds it won't recognize it anymore.
I'm assuming that this is some sort of card contact issue, but I have no idea what I'm doing to cause it to succeed.