Well... its not exactly this way... this is a very usual misconception about the weed.
The weed contains some cannabinoids (mainly THCA) that are indeed ineffective, but they are transformed in THC when heated. So, heating properly the weed increases its amount of THC.
BUT the psychoative cannabinoids (THC, CBD, etc) are active even without heating. They dont need to be heated to get you high.
So, heating the weed can indeed make it stronger, but its only because it increases its amount of THC, and not because it alters (activates or whatever) the THC itself in any way.

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"Everything we do, everything we are, rests on our personal power. If we have enough of it, one word uttered to us might be sufficient to change the course of our lives. But if we don't have enough personal power, the most magnificent piece of wisdom can be revealed to us and that revelation won't make a damn bit of difference." Don Juan Matus - Tales of Power