The end of the mission is always when the player hits Escape. Trust me on this. Always. The missions do not end after the "Mission Success" message, the player ends it. Even if you get killed and there is a black screen, you must hit Escape, and even if the missions fails you must press Escape to end the mission. To be clear- YOU are the one who "ends" the mission. The game doesn't do it.
"Mission Success" or "Mission Failure" does not define the end of the mission. If the sim did end the mission after "Success" then you'd never get a chance to do anything else, do you see? So the sim doesn't end the mission. It's not well documented in the manual, but that is how it works. You're doing nothing "wrong", it's just not been clear that you will be pressing Escape to end the mission
Getting a "Mission Success" or "Mission Failed" message depends on the parameters set by the mission itself, and can be influenced by things other than the player's actions. Sometimes, "Mission Success" can only be generated by landing at your base. It depends on the mission builder's taste. And the mission builder can also make a mistake, making a mission that is impossible to Succeed in, or making a mission that will take hours and hours and hours to get Mission Success because of some element not working right.
Your sentence " I am getting frustrated by spending the time to accomplish the goals only to find I have to do it all over again. " tells me that you have "No instant success" turned on. "No instant success" is the strangest option in the sim
It prevents you from progressing through a campaign unless the primary mission goals for the campaign mission you're flying are all met. Some people insist on flying "Full Switch", which means all switches in the difficulty screen turned on
This is not quite right. No pilot ever got the chance to fly a mission until he got it right. It's Unrealistic
You can't change the difficulty in the middle of a campaign unfortunately, but this is why you are flying the same mission again and again and again
This difficulty option is completely bizarre.