The majority of approaches are flown as "possible" missed approaches. You are cleared to land, but you know that if you do not establish visual contact with the runway by your decision altitude, you will not land. This is the legal and safe approach to IFR flight. ICAO rules require that you must see the runway environment (runways, markings, approach lights) at a specified altitude to continue toward landing. If you do not, you must climb away immediately.

The decision point depends on the approach type. On a precision approach (ILS), you have a Decision Altitude (DA), typically 200 feet above the aerodrome elevation. At DA, you must decide: land or go around. On a non-precision approach (NDB, VOR), you descend to a Minimum Descent Altitude (MDA), which is higher, often 500 feet or more. You level off at MDA and continue to the Missed Approach Point (MAPt). The MAPt is the point along the approach at which, if you have not established the required visual reference, you must initiate the missed approach procedure. On a precision approach, MAPt coincides with DA. On a non-precision approach, MAPt is defined by a fix (DME distance, VOR radial crossing, or timing from the final approach fix). You brief this before descent: "We will not land if we do not see the runway by [altitude/MAPt]."