If someone actually managed to score right on the midpoint for all the dichotomies (*), it probably means one of the following:
1. They answered the way they wish they were
2. They answered the way they think others want them to be
3. They answered the way they are in a specific situation that may require them to act in a non-preferred way (a.k.a. work).
4. They don't have a strong awareness of your own motivations, or have a selective memory of their own behavior.
5. They may have been stressed, tired, angry, depressed during the testing (these emotions tend to push people into their non-dominant functions as a means of trying to cope with the situation).
6. The test is not perfectly able to determine type even under the best of conditions. Many believe its simply the best we have so far.
This is why we have trained professionals verify type after the fact for any legitimate analysis.
As far as being balanced on any activity, think of each method of behavior as a chain of neurons in your brain. You are genetically predisposed towards one chain because it is easier (the odds of have two neural pathways of equal ability are astronomical, and still irrelevant). Your brain favors that pathway, so it starts to develop it the way that brains do. The more you use it the stronger it becomes. The other pathway is still accessible (unless you have a real mental illness that makes using one pathway very difficult, such as autism's effect on extraversion and psychosis on sensing) but less likely to be used as much.
Growing up people can be pressured to favor the less able pathway, but generally the pressure is not complete enough to cause any kind of permanent change. It just inhibits the growth of both functions as they end up being used at times that do not fit their use and can both end up as underdeveloped, or develop in unhealthy directions. If you keep telling an extraverted kid to sit down and be quiet, eventually he's going to attempt to introvert himself at times when extraversion is required because he's developed a mental block on his preferred function.
Healthy type development is the ability to use all your functions when the situation demands, but relying confidantly on your dominant functions to regulate your life.
