I agree about subconscious expectations but could also be due to level of lucidity. Your levels of awareness both conscious and subconscious can contribute to your level of control. Some dreams you will have more access to your subconscious allowing you to achieve more and some dreams you won't. Picture it like 2 overlapping circles, one is your conscious and the other your subconscious. As they drift apart you get more conscious awareness (too much can make you wake up) with less subconscious action. As they drift closer together you get less conscious awareness and more subconscious (i.e. less lucidity). There is a happy balance that can be achieved unfortunately there's no easy way to gauge it.

consciousness-diagram2.jpg

When it comes to remembering your goals a good practice to put in place is to always pause for a second in your dream to remember your goal. If you make this a habit then you will always remember your goal. Some people have a routine they go through whenever they become lucid which looks like this: Pause > remember goal > (optional) stabilize > (optional) increase lucidity > proceed with goal.