It is the privilege of novelty to displace what’s already there. The new generation replacing the old. One goes, the other stays. Every new thing eventually ages and joins an endless cycle of succession.
In the realm of ideas, new ideas don’t always replace the old. Historically, human societies have always been fundamentally conservative, and for their own good. A new practice, a new custom, a new god, a new idea was regarded with suspicion by the members of the community. In the medieval West, novel was synonymous with dangerous and potentially pernicious. The old enjoyed the benefit of age, of survival, of proved and established effectiveness (for the community or one of its groups). New ideas were unproved, they could or couldn’t work, they were a gamble. And culture is quite risk-averse when it comes to survival and transmission.
When the French thinker Peter Abelard arrived in Paris around 1100 to study philosophy and theology, he ended up clashing with another philosopher and his erstwhile teacher William of Champeaux. Their forceful debates over the nature of language and its relationship to reality drew an instant and vociferous crowd. Abelard’s novel way of reasoning, which jumpstarted the scholastic age in Western intellectual history, proved far popular than William’s traditional approaches. The established order was threatened and, as people always do when they feel threatened, they threaten violence in return. Abelard left Paris (moving nextdoor in Melun, though), but his ideas stayed. They germinated in Paris and elsewhere to the point that by the end of the twelfth century, the Abelardian way became the benchmark in dialectical reasoning (logic!) and philosophical reflection. Scholasticism was born.
The new ideas drove out the old, even though the new guy had been driven out of the city.