Running for president is tough if you haven't been anointed as one of the likely heirs apparent. People don't want to donate money to a candidate that won't make it through the primaries.
Being a third-party candidate in our primarily two-party system is tough in the actual election. People don't want to "waste" their votes when they only have one to cast.
Pitching new ideas to colleagues is challenging if they don't believe what you're proposing has any chance of succeeding.
People need to see a reasonable percentage of possibility if we hope to get their commitment, their money, their vote, their support.
Too many leaders forget this important point yet are still surprised when their "brilliant" ideas don't seem to get any traction.