A few months ago, I posted two quotes about how science works, and why it's effective:
The first principle is that you must not fool yourself—and you are the easiest person to fool. - Richard Feynman
If common sense were a reliable guide, we wouldn't need science in the first place. - Amanda Gefter
Feynman and Gefter sum up what makes science different from many other intellectual pursuits, and why it has so radically changed the human experience over the past few hundred years. Not fooling ourselves turns out to be surprisingly difficult. That's because (to dig up another thing I write about frequently here) our brains aren't built to find the truth. Often, we have to work against our own thinking to do that.
We evolved to get by and reproduce as hunter-gatherer primates on the savannah of Africa, not to follow two or more independent lines of evidence to confirm how fast the universe is expanding. Yet we have figured that out, because scientific thinking is designed to counteract our tendencies to fool ourselves. Sometimes we still do, for awhile, but science also tends to be self-correcting, because it tries to force reality to trump belief.
There's an excellent article in the current issue of the academic journal Evolution: Education and Outreach, titled "Understanding Natural Selection: Essential Concepts and Common Misconceptions" (via PZ Myers). Yes, it's academic and thus (for a web page) pretty long, but there's lots of meat there, and it's written for a general audience. It's worth reading through.
The first part summarizes how natural selection works. The second part asks "why is natural selection so difficult to understand?" After all, it is elegant and logical, and has mountains (literally, in some cases) of evidence behind it, collected and analyzed and correlated and compared and verified over 150 years. However:
Much of the human experience involves overcoming obstacles, achieving goals, and fulfilling needs. Not surprisingly, human psychology includes a powerful bias toward thoughts about the "purpose" or "function" of objects and behaviors [...] the "human function compunction." This bias is particularly strong in children, who are apt to see most of the world in terms of purpose; for example, even suggesting that "rocks are pointy to keep animals from sitting on them".
In other words, one reason it's hard to understand natural selection (or quantum mechanics, or the weather, or geological time) is that we're predisposed to believe that the whole universe is like us.
Indeed, that's often not a bad place to start. Seeing that populations of organisms change over time, early evolutionary theorists proposed that the organisms changed, in effect, because they wanted to, and passed those desired changes on to their offspring. But those ideas had to be discarded when the evidence didn't support them. Similarly, long tradition indicates that many alternative medical therapies might be worth examining, but research shows that most of them don't work.
Intuition and common sense are a good way to find your way through day-to-day life, but they're not especially reliable when trying to figure out how reality works, and thus how to do things that are genuinely new.