Doubting my Lack of Self Doubt

It's less than 2 months until we fly now and I've been enjoying reading a few books about others who've taken on long term cycle trips.  We're going to make a useful links, book and kit review tab where you'll be able to get more details on these sorts of things, but we've not made it yet.

One of the things I've noticed most about the others who've undertaken major cycle tours alone is that they seem to be beset by a lot of self doubt about being able to complete the trip which probably weren't helped by having friends, family or colleagues telling them 'you can't do that' or 'you'll never make it' or other such nay-saying.
I don't feel like that at all.  Neither does Tom.  But reading these accounts of these capable guys feeling all this self doubt makes me doubt my lack of self doubt!
It makes me wonder if we're too naive or don't understand what we're up against, but I don't think so.  We're both very confident that we'll be fine.  Our mini-tours have been a huge success and we've overcome any hurdles or hardships without falling out or falling apart.  I wonder if having a loose plan and no actual end point helps, we're not doing it for charity or to break any records and we're not trying to prove anything to anyone, we're just going out to have an adventure and see some of our wonderful planet.  Overall I think we'll cycle at least 24,000 miles which turns out to be not far off the circumference of the earth which is 24,902 miles at the equator, yet somehow saying we're cycling around the Americas sounds less far and easier than we're cycling around the world.

I think that doing it together helps too.  We both respect each other a lot and trust in our capabilities and so when one of us is feeling bit low or doubtful the other can counter this with encouragement and enthusiasm to get us back on track and raring to go again.
We've also been very lucky in that of all the people we've told our plans to - friends, family, colleagues, random acquaintances, medical professionals - no one has said 'you can't do that' or 'you'll never make it'.  The closest we've got to anyone doubting us is the nurse we first spoke to about injections who when discussing our probable route through South America being through the Andes said "oh you're good at cycling up hills are you?!" in a somewhat mocking tone to which I replied "well not so much now, but by the time we get to South America we'll have about 12,000 miles under our belt and will have crossed the Rockies so we should be fine by then".

Tom's biggest worry is us actually getting in to the US in the first place, which is a bit of a worry, but I feel like we'll just do what we can to help them to let us in and if they say no then we'll make a new plan and have an even more spontaneous adventure.
So thank you to all of you for not doubting us - its going to be such an incredible journey.