For very many years, in steam and diesel loco days, the Inverness to Kyle of Lochalsh line had two westbound and three eastbound passenger services per day. There was an element of shunting of passenger vehicles, and interchange of locomotives with freight services, that allowed this.
It's not necessarily true that the traffic pattern in one direction is reflected in the other. A current example is what has happened on the LTS line, where for morning commuters in to London it can be most efficient to change at West Ham onto the Jubilee Line onward to the West End etc. In the evening passengers returning this way will not get a seat, and sometimes cannot even get in the overcrowded train, so they return via Fenchurch Street to board their train at the start.
It's not necessarily true that the traffic pattern in one direction is reflected in the other. A current example is what has happened on the LTS line, where for morning commuters in to London it can be most efficient to change at West Ham onto the Jubilee Line onward to the West End etc. In the evening passengers returning this way will not get a seat, and sometimes cannot even get in the overcrowded train, so they return via Fenchurch Street to board their train at the start.