When I compared people that take on big goals later in life with those who simply simulate them in their mind, then decide their projected end results are 'predictable and uninteresting', I saw something interesting.
Those who take on big goals are seen as naive and almost childlike, because the 'experienced' believe they already know the end results.
Those who don't take on big goals get to be in the audience and throw stones, but never really amount to anything other than gloating at a possible failure.
I think the experience works against you at a certain age. The projections are a lie, or possibly inaccurate at best. I've come to believe you don't know what will happen until you do it -- what your mind simulates is often only correct in the broadest sense, but way way off when it comes to the important details and compound ramifications.
In otherwords, keep taking on big goals and press on to finish them, while ignoring that pesky voice which thinks it already knows how this will all turn out. And ignore the people who do the same, their words are rarely helpful.