Why do so many Christians think their religion is the oldest and truest?

Truth about a subject does not make it a *foot in mouth* problem.. Yes, MOST of the *traditions* of holidays and even most *religious traditions and practices* are of pagan decent and origin.. Just the way and truth of it... However, the reason behind the adoption of them are meant for Godly reasons... and it is not really that some are ignorant, it is they may just not understand the history or it is just hard for them to admit... but, as a Christian I don't see why.. It all is for Gods glory, not mans !!!! go in peace.... God bless