Positive Re-enforcement.

Your body has an incredible ability to learn and remember.  Fitness Professionals know this as the SAID principle

Specific Adaptation to Imposed Demands.

To illustrate, imagine having your arm in a sling for six weeks.  Your body will "learn" that a bent, unmoving elbow is the "demand".  As an adaptation, it allows the muscles in the front of the arm (biceps) to shorten, and the restricted muscles at the back of the arm (triceps) will weaken.  

Several weeks later when you remove the sling, your arm will of course still have the same muscles, but they will have adapted to the shortened, weakened state. Your arm will not extend very easily because of this.   Is this a permanent condition?  Luckily, no.  

By gradually increasing movement, your body will again adapt to the new demands by gaining strength and flexibility..   

But, what does this mean to you?

If your fitness program includes correct movement patterns (often referred to as "good technique"), and you gradually increase the demands on your body while using those patterns, you can teach your body to operate at a peak level of efficiency.   On the other hand, if you repeatedly use faulty movements (poor technique), which are often compensations for specific weaknesses, over time, your body will adapt to inefficient movements which can ultimately lead to injury.

While this can seem like a complicated topic, it can be summed up as follows:

Reinforce CORRECT movements