When You Don't Want To Think and Why
I'm paraphrasing a quote from HugS here, who was being very insightful about the mental aspect of this game. He said something similar to this:
"You don't want to use mindgames against somebody who doesn't have them, because they may catch you off guard with randomness."
The heart of this idea is that part of mindgames is knowing how skilled your opponent is. How good they are determines how you should think during your match.
For instance, why would you play differently against a computer than you would against a human? Simple answer: the computer does not adapt. No matter how many times you charge a forward smash, the computer will run into it. You do not need to think while playing against a computer because the same thing will always work.
Some people play like computers, and it is useless, even hurtful, to try and outthink them. If they do the same thing every time, and you know how to counter it, why would you even worry about outthinking them? Just wait for them to repeat a move and then punish them. If your opponent always throws scissors, would you suddenly throw paper just to mix it up? No! You'd throw rock until he learned that he has more than one move available.
Even as people learn advanced techniques, some still remain predictable. Maybe your opponent always tries to shield grab you. You always dodge right when you land, and he always tries to shieldgrab, and he always misses, and he never learns. You aren't obliged to mix up your strategy for the sake of being an advanced player. You cut to the heart of the matter and say "I know what he's going to do, and I'm going to do the same thing over and over again if he's never going to catch on."
As your opponent improves, your mental approach needs to change. Let's say your opponent catches on to your favorite movement strategy one minute into the match. If you can recognize his skill and anticipate when he is going to "catch on," then you can change at the exact moment he thinks he has you.
This mental skill is part of what makes playing this game so difficult. I can't just watch you and see how frequently you miss L-cancels or short hops. I need to watch you and learn--sometimes very very quickly--how you learn during a match. Some people are naturally good at this, and some people have to play a large number of opponents before they can recognize different skill levels. I will try and formulate ways to improve in this area, but for now all I can really do is identify it.
The ultimate example of this is a friend I used to smash with: he would often perform better against more skilled players than he would against newbies. This is because he always believed that his opponent would be thinking during the match as much as he did. He would complain that he just lost to a scrubby Marth or Peach who spammed the c-stick and was "incredibly predictable."
If they were so predictable, why didn't he just play to their level? Why didn't he play patiently and wait for them to do the same thing, then punish them, then do it a few more times until the match was over? The thing is, my friend was more interested in playing like a good player rather than being a truly skilled one. He didn't identify his opponent's skill, and he was unable to figure out how he should think during his matches. He placed poorly in a lot of tournaments because of this, and it made him incredibly mad.
The lesson is this: before you start trying to outthink your opponent, figure out how smart they are. If you don't need to think hard at all to beat them, either because they are very predictable or because you're too fast for them to touch you, then don't waste your energy thinking. If you only need to mix up your playstyle occasionally, then periodically switch styles. If you have to play like a different person every ten seconds in order to outfox them, then so be it. Your method of thought should be determined by your opponent's skill level.