"the shave follows a definite and predetermined pattern"

As with every other aspect of Frank’s life, everything is about patterns and ritual. It is possible that this could be a slight obsessive compulsive disorder with Frank, as a way to curb his anxiety about his situation, despite him claiming that he is perfectly happy.

"In OCD, the sufferer experiences intrusive thoughts (the obsessions) which are the source of anxiety. However, the anxiety can only be relieved by performing an often ritualistic act (the compulsion).  Common obsessions include germs or losing things. The compulsions for each of those may include washing for germs or arranging and grouping objects for losing things. However, the compulsion does not necessarily have to be logically related to the obsession. The only requirement is that, for whatever reason, it relieves the anxiety generated by the obsession". Click here for the source.