Before scientists can identify something as theory, they have to gain overwhelming evidence through scientific investigation. And any good theory is only one good experiment away from being rejected. That is, scientists must be able to imagine some set of results that would cause them to reject, or falsify, the theory; then they must see that over and over again. The factor that makes a science a science is the adherence to the scientific process:
Make observations about the natural world.
Formulate a hypothesis.
The hypothesis serves as the scientist's starting point; maybe it's right, and maybe it's wrong. They key is to do enough testing to find out.
Gather additional data to test this hypothesis.
As your data accumulates, it either supports your hypothesis, or it forces you to revise or abandon the hypothesis. Remember: The hypothesis scientists come up with must be falsifiable. That is, scientists must be able to imagine some set of results that would cause them to reject the theory, and then they must test those ideas out.
Continue testing (if the data from Step 3 supports your hypothesis) or revise your hypothesis and test again.
After an overwhelming amount of information accumulates in support of the hypothesis, you elevate the hypothesis to a theory.
If, at anytime in the future, new data arises that causes you to revise or reject your theory, then you revise or reject it and start again at Step 1.
Real scientists never ignore facts or observations in order to protect a hypothesis or theory, even one that they're particularly fond of.