Rocketman describes what it took to get to Mars. Read the whole thing. The Spirit rover was at different stages in its life a massive flying bomb, rifled projectile, pirouetting dancer, meteor, paratrooper and beachball before it came to rest on the Red Planet. And then we got to know if it worked.
The enormous amount of energy required to get landers all the way to the Martian surface imposes severe restrictions on the design of the vehicles, which is why it is no easy feat to have a successful mission. There are a lot of critical systems that have absolutely no backup, and if one of them fails, the whole mission will fail. Which is why every component, system and subsystem on a planetary probe is rigorously tested prior to launch, and it is also one of the reasons why these types of missions cost a lot of money.
Rocketman clearly describes why a certain percentage of failures are to be expected. Is the expense worth it? Pictures of soil disturbed by the retraction of airbags show a surface that resembles mud, in a place where the presence of water is wildly improbable. Something is holding the topsoil together like play-doh and there is no obvious terrestrial explanation for it. Mars is truly another planet. And if it is anyone's it is man's. The story of Mars, its forgotten geological history and its very fate are now part of the human story. Only we will weep for it. Only we will laugh on it. Only we will remember it.
Then felt I like some watcher of the skies
When a new planet swims into his ken;
Or like stout Cortez when with eagle eyes
He star'd at the Pacific—and all his men
Look'd at each other with a wild surmise—
Silent, upon a peak in Darien.