This is something that troubles me too.
Why are we, as entrepreneurs, so optimistic about our growth during the first stages of our businesses? We overestimate what we can do in 1 year, but underestimate what we can do in 5-10 years.
The pain of experience teaches you to be wiser with projections for years 5-10.
Optimism is not bad but it needs to be based in reality. Most plans/projections/assumptions written by inexperienced people are yikes in the extreme with the items that get over-looked.
it's human psychology
it's not specific to business/startup/...
it could relate to one, two, three, too many perception
might also relate to the marshmallow test
or the feeling of control...