Sometimes someone who's trained longer will lose to someone who's trained for a shorter time. You'll see blue belts giving purple and brown belts a hard time, and you might wonder how someone with around 2 years of training, sometimes less, can do so well against higher ranked people in the gym, and often do very well at competitons. The reason is not necessarily that they are better at jiu-jtisu, the reason is knowledge imbalance. Yes traditionally blue belts tend to be 20 year olds with all the muscles and cardio, and brown belts... not*. But that isn't the reason, trust me, it's knowledge imbalance. More importantly those guys tend to do well at competition also, where extreme physical/age advantages are removed.
Knowledge imbalance means that these athletes know a technique, or in reality a sequence of techniques far better than their opponent. Complementing this depth of knowledge for attacking a sequence of techniques, is their knowledge of all the common defenses. Defenses employed by someone who has no idea what's happening, defenses employed by someone who has a vague idea of how to defend the technqiue, and finally, defenses they themselves would employ to shut down those techniques. These people will pit their depth of specific knoweldge against their opponents' breadth of shallow knowledge. Or to put it another way for military tactics buffs, BLITZKRIEG.
Blitzkrieg /ˈblɪtskriːɡ/ (German pronunciation: [ˈblɪtskʁiːk], from Blitz ["lightning"] + Krieg ["war"]) is a method of warfare where the attacker spearheads an offence using a rapid overwhelming force concentration.
A good example of one of these techniques is berimbolo, which is actually a sequence of movements used to get from De La Riva guard onto someones back. Other famous sequences are 50/50 and worm guard. If you follow lower belt competition, you will always see the berimbolo dude, the 50/50 chick, who always storm through the bracket, employing the same sequence of attacks in almost every match.
As you move up the belt ranks, towards brown and black, this knowledge imbalance almost always disappears. By the time you're a brown or black belt, even if you don't yourself play berimbolo, you should know enough about the technique to shut it down. It doesn't always disappear and a few people have used the technique to varying degrees of success at high level competition. Here are some examples:
Tarik Hopstok -- Tarikoplata
A lot of very good, and experienced people lost at purple & brown belt to Tarik, because they had no idea of the danger, defence or counters to the Tarikoplata sequences.
Danaher Deathsquad -- heel hooks
Danaher is very open about how he gives his students a large depth of knowledge in the very small area, that of heel hooks, and creates this imbalance, compared to all the other top level no-gi competitors.
At lower belts, focusing on a specific technique can lead to a lot of success in the gym and at competition. While other white and blue belts are still figuring out how to pass the guard, how to escape from mount, how to hold side control, you skip all that by only playing De La Riva, Berimbolo, reach the back, get the tap. To a certain extent the technique doesn't matter, and you should pick something that you like, that fits with your body type. There are a few common techniques and positions that your opponent will have seen so much that even if you have a deep knowledge and understanding of that position, it won't be enough to overcome their experience of the position. For example closed guard.
Hopefully this explains how blue belts can give purple and brown belts a hard time. The roll is actually an exhibition between someone who's trained berimbolo for 2 years almost exclusively, against someone who's trained jiu-jitsu for 6, 7, 8 years, but has only spent a few classes on berimbolo, and gained some general experience over the years defending it.
There is obviously a down side to this tactic. If your knowledge and experience of your chosen technique isn't deep enough to overcome your opponents defenses, and they can move the game into an area you are not familiar with, it might be game over. That's the fun of jiu-jitsu though.
If you do decide to focus on a specific technique, you should try and play this position and improve it almost every time your roll. Stay after class and practice the techniques, study it on youtube, instructionals etc. And if you really want to accelerate your way to becoming someone the higher belts start to fear, get some private coaching from someone who uses that technique at the highest level of competition, for example Paquito's spider guard, or Bradley's omoplata. These instructors will be able to give you details that they've spent years learning, that work against other top level black belts.
* the demographics of higher belts are changing, higher belts in their 20s with cardio are becoming more common.