Drilling/digging on Mars a sh*te harder than it looks
Lest anyone think that Drilling or Digging on Mars was an easy Topic imagine this - you have to select the type of drill your going to use based on a guess of what material you will find on Mars. A few years later when you actually get to Mars, you have to guess how hard the rock is that you want to drill and what it's made from based on Pictures taken of the outside surface. You then have to set appropriate speeds and feeds such that a) you can drill in the rock, and b) if you're wrong about the consistency or that directly below the surface there is some harder impurity or the like that you wont destroy your bit. And you have to program this with enough feedback loops to do it autonmously, because you cant manually stop the drill if something goes wrong. At least not for 28 minutes (14 minutes for notification of the failure to get to Earth and 14 minutes for the big Stop Signal to be sent back).
To put that in Earth Terms - imagine you have to select a drill bit to drill a hole in the wall of a house that you havent seen and the best you can say is that the house is in, for example, Belgium. Then you have to select the right feeds and speeds for use of that drill based on a photo of the wall. Do you take the masonry bit knowing that most walls in Belgium are masonry, but also knowing that if you hit a metal stanchion you're screwed? Or do you take the carbon steel bit knowing that you can probably cut through anything, but that you are likely to damage the surrounding areas and damage the science you want to conduct in those areas?
The Boffins working on these things deserve a huge round of applause (and a pint) for their great work making these operations so successful!