My 2D objects won't collide at all. Help?

I have a 2D Project
added 2 Sprites via GameObject → Create other → Sprite
added Rigidbody 2D & Box Collider 2D to the moving one
28074-unbenannt1.png

added Box Collider 2D to the static one
28075-unbenannt2.png

did not change any parameters of the components
Test it: Box won’t stay on platform
added Script Component with OnCollisionEnter(Collision2D coll) with Debug.Log(“WTF?”);
Test it: no collision, no “WTF?”

…WTF?
It supposed to be a box falling onto a static platform

Due to the small size of the colliders the physics engine skips the position just over it, making the colliders bigger solves this issue.