Is culture very hard to change?

Is culture very hard to change? Alistair Cockburn says “the culture becomes increasingly hard to change as the #ppl increases. .. It is for this reason, that I have been so adamant in the Heart of Agile organization that the tone of interactions and the developing personality of the org is the single most important thing to me.”

But, on the other hand, Daniel Mezick says you can change the culture in a few…