There are feelings and there is logic. Wanting to do something generally comes from an emotional feeling wanting to be met. However the mind presents logic opposed to it. Or the situation may be in reverse. The action generally is caused from whichever is stronger at the moment.
This does not excuse behavior, it only explains it.
Let's say there is a woman who claims to want to remain faithful to her husband. The woman cheats anyway. In her mind she knows that she wants to make her husband happy by remaining faithful. This is a logical thought. However she has been overcome with an emotional response that forced her over the edge.
A man is called into the office for something he feels he didn't do wrong. The boss starts degrading him and telling him he messed up. Now the boss is not firing the guy. The boss may even have very valid points. Maybe the boss is full of crap. Either way the man gets upset because he feels that this is a personal attack. It could be a personal attack or not. Either way the man decides that his feelings are being hurt. Now in his mind he is going through emotional checks and balances with his logic. The logic states that he has a wife and kids, car payments, and a mortgage. This is part of forethought and oversight. That is a whole other topic.So in this case he decides internally if he can withstand the trauma to his emotions to keep his logics working as they should. He decides that because this only happens once in a while he will be OK. So he listens and keeps his job.
In one example the person decided to go with emotion because it overpowered the logic. In the other case the logic overpowered the emotion.
In most movies where robots rule the world the humans are destroyed because of logical reasons. We as humans generally find that to suck. We all are at some level mainly ruled by happiness, instincts and some other prime directives.
Here is what you really wanted to know
So if you have a logical reason to want to do something that you know logically will improve your happiness it will still be hard to do. This is because of safety mechanisms as well as other emotion responses. These emotional responses will hinder your ability to use that logic to progress yourself towards your action.
Let's say that Joe wants to become better with women. He knows he wants to do this because he knows that women excite him and induce an emotion response inside of him that he enjoys. He knows that he can find a partner this way which will also make him happy. He knows that if he ever wants children he may want to find a woman to mate with. All of those things are awesome to him. However to do so he has to become better with women. To become better with women he must go into action (use a logical pattern) and fail miserably many times with women until his subconscious is able to form methods of interacting that will make him more desirable to talk to and be around. At this point his mind is saying, "This is going to take time, money, induce frustrations as failure does to a human, be degraded many times over, still be lonely, and possibly get beat up by a boyfriend."
Now in this example some of those reasons the mind creates are pointless while others are valid. Even if the reasons are not valid they are assigned values. The mind then decides based on those values which has a higher value. Generally if you are ingrained in a lifestyle that is directly inverse of the lifestyle you wish to have the change will be difficult as the mind will assign large values to the negatives vs the positive sides.
So when wanting to do something because you know it will induce positive value in terms of happiness (which all that matters in life when you expand this concept to the enormous proportions that the mind does... even in terms of eating...)
In order to counter the negatives the mind conjures up you have to fabricate more positives. You have to dig deep down and pull out all the stops until the positives you have fabricated or found deep inside yourself outweigh the negatives the mind has subconsciously presented. When you do this... then you have to force your mind to activate a full force attack on your action and actually go into action.
KNOW THY SELF AND LET IT BE KNOWN THAT THY SELF IS STRONGER THAN YOUR FEARS.
I will hereby add to your list of positives.
Courage is overcoming your fears. Courage is super fucking sexy. Courage adds to your self-confidence and self image.