It's easier to comprehend the forces that wear down mountains, such as mass wasting, wind and frost erosion, and so on, than to conceive of the tremendous forces it takes for mountain formation.
Maybe this is because the forces of erosion are usually on a fairly small scale, and we see it happen quite often, thus it's pretty easy for us to wrap our minds around.
Mountain building forces, however, are usually on a huge scale. For instance, imagine a tectonic plate, the size of a country and 30 miles thick, running headlong into another, crumpling under the force and folding upward (talk about a fender-bender!). This is the way a lot of the world's mountains are built. There are other types of mountains, of course, like volcanic, and most mountain ranges are the product of more than one mountain-building process.