I agree that it is mental, 100% mental. In this forum we have the support we need to continue through those mental hurdles. It is something I tell my wife every day. We ride together and sometimes when we get to certain spots on our typical route she will say, this is where I die. I have to remind her that she is losing the mental game and to get past it because she is not breathing hard or working hard, its mental.
Why is it 100% mental? The decision to even think about ever hopping on a bike is mental, that decision happens before you even walk into the bike shop. That fear of the unknown keeps people from even considering walking into a bike shop. I consider myself extremely mentally strong, making the decision to change my life through cycling and dragging my wife along with me was very difficult, but I am so happy we are doing it.