Lately, I've been realizing what a hell of an amazing job it is for NASA scientist to explore mars. For a probe to be able to study the air on mars, or pick up a rock, scan it, weigh it, etc, entirely from remote controls back on Earth must be tiresome, because if you can't trust the robot enough to do a good job if it can't go up a 10 inch step, unless you physically go to mars and dragged the probe up on that 10 inch cliff yourself. To explore a terrain entirely through probes is challenging enough. And each probe takes years and money to create and is a hassle to launch, so you can't just casually send the next toy in line to mars when a probe accidentally falls into a ditch. And if you did have a large supply, chances are it won't land in the same place where the last probe died in.