Lack of random environments

Or for a more everyday example, look at some of the domesticated animals and plants we've produced. We've produced all manner of beast completely incapable of surviving in the wild - to serve as more effective foodsources, to perform some task for us, or just because we think they look cute. Many carry traits that would be catastrophic in most environments and heavily selected against, but they exist in a very unusual environment where the primary selective factor is human intervention. We've even bred organisms completely incapable of independent reproduction but, in the very specific environment of, for example, a pigeon-fancier's coop, they're the fittest organisms.

Alfred's way of putting it was exactly correct - mutations are random in respect to fitness. This is what we mean when we talk about random mutations. The processes which cause mutations may well be deterministic and predictable if we had sufficient knowledge, and we know that they are more likely to happen in certain conditions - being bombarded with radiation or exposed to mutagenic chemicals, for example.The randomness is in the sense that you cannot predict what mutations will occur by knowing what would make the organism more fit - mutations happen randomly with respect to fitness.