(And even if we had never done it, that is not a barrier.) The only thing we have to fear is despair. We are wealthy, young, capable and powerful; we can accomplish enormous things. No wonder the status quo loves to spread despair - they have no other defense: Imagine if people left behind all that despair and started acting!
Yes, the concept is that simple, and the action needed by you and me is that simple. Just forget all the doubts and just get to work!
(I don't mean to berate you with the exclamation points. I'm excited by the possibilities. LFG! :) )
If you want to grasp how that could happen, it's just people following social norms. The norm is despair: if you are in a meeting and everyone says such-and-such is hopeless, raising your hand and saying otherwise is not only socially hard but a bit transgressive. My hypothesis is that the status quo powers political messaging has pushed despair - after all, what else will preserve the senseless, unpopular status quo (look at climate change!)? It's the only defense they have.