Ignorant mind and Buddha nature I read in a Mahayana Buddhist book (insight into emptiness) 2 concepts that I find hard to reconcile:

1- Our minds used to be pure, only Buddha nature, and got contaminated with ignorance that led to attachment and it makes us cycle in this cyclic existence.

2- We all have and always had Buddha nature in our minds.

My question is: how could a pure mind with Buddha nature get contaminated in the first place? I can't understand how "Buddha nature" could let itself be tricked by ignorance, sounds strange, sounds like a "Big Buddha failure"!

Unless...Buddha nature means only a distant background on the mind, something weak, that has no power to act by itself, weaker than the aggregates, but it doesn't sound like that. (!?)

Can anyone help?
It seems like you're viewing buddha nature as essence. Freedom from imputations, conceptions, conventions, perspective, etc is buddha nature. But don't view it as essence, which would be a perpetuation of imputation of self and precisely what we are trying to avoid. Hope this helps.