It is important that people understand how a 2x2x2 mechanism works to avoid issues with them. 2x2x2s have a fixed corner, on some 2x2x2s this is done by the core itself trapping a specific corner in place while on others, like the one in this video, it is done by having 3 of the 'edge' pieces having an extra bit which allows them to trap a corner in place. You must never attempt to force the fixed corner to twist as this can cause it to be permanently deformed.

Cube used in this video