Strange shadow over my mesh I'm a beginner, I started learning blender a week ago, I followed a lot of tutorials on youtube on how to fix and prevent some common beginner problems, but I really don't know what's is going on on my mesh.

Since it is hard to explain I made a little video showing the problem on my mesh: http://sendvid.com/flt8t55s

I already checked for doubles, already recalculated normals.

If I apply a Subdivide Surface modifier all those strange shadows disappear and everything appear smooth, but from what I've learned so far, it is a bad thing to use Modifiers to fix some of the problem that shouldn't be there.

So I want to know what's could be the problem.
It appears to me that the normals should be recomputed. In Edit Mode select all vertices with "A" and recalculate the normals by Ctrl-N. In addition, you may use "Smooth" from the toolbar in Object Mode to "smooth" the object. But that depends on how it should appear in general.
The vertices appear to be slightly "shifted", such that this kind of artifacts can happen. For me, it's completely ok to use the subdivide modifier. This modified subdivides all faces and reduces the angles of each of the faces.