The larger a project (either in space or in time), the less amenable to predictability it becomes. If I am to walk within my 4 meters radius apartment. Say from the couch to get some black coffee for my craving brain. There are fewer things that could go wrong, compared to if I will be traveling from my *rusty apartment in Georgia, all the way to Zhengyangmen in Beijing.
Not to say it is impossible for the latter to be successful and the former, unsuccessful. No, not at all. However, stochastic probability tells us that the likelihood of success in the latter dwarf (exceedingly) to that of the former.
Why?, because of the variability of the variables.
Hence, the same modus operandi or level of optimism used in predicting your upcoming summer vacation should not be used to predict exactly where you will be 10 years from now.
Friends, life is non-linear.