The default was on easy difficulty there are 3 difficulty levels that can be changed under the Options menu.
(Yeah an odd place to be and the plan is to move it to the contract when you start.
1. Easy: Blocks snap to place and comes static after placement.
2. Normal: Blocks snap to place but remain dynamic.
3. Hard: Block don't snap to place and they remain dynamic so it's quite a challenge to stack the peaces.