The reasons for failed reality checks are several. You may be new to reality checks in general, and thus not looking closely enough. You may be new to the "finger/hands" reality check, and thus not looking closely enough.

Or you might just've had an off night, that happens.

I recommend you stick to more concrete reality checks, in favor of or supplementary to the "finger/hands" check. I've never heard of a story where the "nose plug" failed, for example.