( CNN ) -- The throaty , thumping churn of the military helicopter convoy is a sound like no other . It 's a common sound in Washington , but less so in the skies over Chicago . Barack Obama does n't get back to his old town much these days . He did last week ; he returned to Illinois for slightly more than 24 hours to celebrate his 49th birthday with some friends , to make a public appearance at an auto plant , to raise some money for upcoming campaigns . And as he arrived late on a wet and cloud-darkened afternoon , there was that baritone rumble of the line of helicopters , there were the Chicagoans looking up toward the president in Marine One , there were the streets closed to traffic in anticipation of his motorcade . Obama arouses in people such political passions , both positive and negative , that sometime it feels futile to discuss him without knowing that the conversation will veer inevitably into heated partisan territory . Yet there may be some usefulness -- especially for those of us not consumed by politics -- in stepping back , on an occasion like one of his rare returns to Illinois , to consider a lesson inherent in his rise : . Aim high . It seems pretty simple , after the fact . Obama is president of the United States . Of course he was ambitious ; of course he set his sights high , in his successful 2004 campaign for the U.S. Senate and then in the 2008 campaign that took him to the White House . Today those decisions of his are , literally , history . But it is instructive to think of him not as the man in Marine One , but as the frustrated 41-year-old state legislator in Springfield , Illinois , in January of 2003 . He had tried once for an office that would move him onto the national stage ; in 2000 he had attempted a run for the United States House of Representatives . He was crushed by a margin of 2-to-1 in the Democratic primary . By 2003 he was back in Springfield , a face in the crowd . He was known to those who follow state politics closely , and to statehouse reporters , but Obama at the beginning of 2003 could have walked into most restaurants and stores in Chicago and not have turned a single head . There were two marquee political stars in the state : the glamorous new governor , Rod Blagojevich , who had just been sworn in for his first term , and the mayor of Chicago , Richard M. Daley , bearer of the most famous name in local government . What was Obama to do ? Bide his time in Springfield , hoping to achieve increasingly more influential committee assignments ? Eventually try once more for the U.S. House of Representatives , after the humiliating rejection in 2000 ? Put his ambitions for elective office away , and take up the private practice of law ? We know what he did instead . Aim high . It does n't always work ; a person can aim high , and fall flat on his face . He can be mocked for even trying , especially when he comes up short . But as Marine One and its convoy thundered over the edge of where Lake Michigan touches the shore in Chicago last week , as the people on the streets looked skyward , a jury at the Everett M. Dirksen Federal Building a few blocks to the west had just completed another day of deliberations that will determine if Rod Blagojevich will remain a free citizen or will be sent to prison . When Obama , before climbing into the helicopter , had landed at O'Hare International Airport in Air Force One , Richard Daley was waiting patiently in the rain to stand in a receiving line and shake the president 's hand . Things have n't been going particularly smoothly for Obama in recent months ; his poll numbers are down , he seems under constant criticism from every direction , his missteps often appear on newspaper front pages and at the top of television newscasts . Why anyone wants the job that a president has is a question that rational people tend to ask themselves from time to time . Yet when we do take that step back from the frenzy of a given day , and consider the choices a person makes during the course of a lifetime -- the choices about whether to be satisfied with what you have , or to take that leap of faith and try for something beyond what the rest of the world thinks you can do . . . . I have a copy of a letter , a public document , that I have held onto since November 13 , 2008 , when it was written . It 's very brief . It was addressed to Blagojevich , who on that day was still the governor of Illinois . `` Dear Mr . Governor : . `` I hereby resign effective November 16 , 2008 from the United States Senate in order to prepare for my duties as President of the United States . `` Sincerely , . `` Barack Obama '' You ask yourself what must go through his mind , in his seat aboard Marine One , as he looks down at the city where he once lived , at the people who live there now , the people peering up toward the chopper convoy 's roar . Impossible things can happen to a person . But first , a person has to try . The opinions expressed in this commentary are solely those of Bob Greene .
Barack Obama was a state legislator whose advancement was blocked in Illinois . Bob Greene recalls Obama rejected idea of staying in place , sought national office . Comment: Greene : People can accomplish the `` impossible , '' but only if they try .