I have a natural gas standing pilot forced air heating unit. I light my own pilot light every year and have never had a problem. I can hear the gas flowing but the pilot will not ignite. I have never replaced any part of the furnace and have lived in my home for 10 years. I do not think the problem is related to the thermocouple because from what I have read the thermocouple is a safety device that controls the valve that allows gas to continue to the pilot light. If I understand correctly, the thermocouple safety feature is overridden by depressing and holding the pilot knob in order to light the pilot light. Given that information, if the thermocouple is bad, then I should be able to at least light the pilot light. I have also cleared the pilot light opening (even though it looked okay). What would cause the pilot light not to light?

You may have air in the line. Try holding the button down longer... And you are correct, the thermocouple has nothing to do with being able to light the pilot while pushing the button. If the thermocouple does not sense flame, it will shut the pilot off or you will not be able to release the button without the pilot flame going out...