By habit, once a decision is made, a brain will continue cooking up more reasons why this action was valid.
"Should I wait for an opening in traffic and turn left or turn right now and come back this direction later?"
You decide to turn right. As it is, you see a friend driving his car and you both wave, thinking, "awesome, it's Matt! I love that guy. I'm glad I went this way." Soon thereafter, you see a dog crossing the road and slow down to let it cross, thinking, "someone else would have hit this dog! Good thing I turned right!"
Turning right had nothing to do with either of these events, unless Matt tends to frequent a particular strip of road where dogs like to cross.
By habit, your thought process works to justify its former decisions. Could you have possibly known these things earlier? No. Did they have anything to do with your decision-making process? No. Are you backwards-rationalizing? Yes.
So what? What's wrong with saying I did a good job?
You want to make good choices in life. A good choice is one made on all the available facts. If you turned left and wound up getting into an accident, you might think to yourself, "Damnit. I should have turned right. Why did I have to turn left? I usually turn right, there must be something wrong with me today."
Front-load your decision making process. Put that extra effort into making the right decision, then make it, and live freely with the consequences. You can spend five minutes justifying your decision to yourself after the fact, or you can spend five minutes doing whatever the you want to do.
Personally, I like looking out the window and watching the trees blow in the wind.