I think where I see the resemblance in a character like Paul Giamatti's in Sideways is in the instance of improbability. (I'd also see myself as Luke Wilson in Old School but...) There are a lot of things in life you want and well, sort of need, kind of equally. Life puts great challenges before you like marriage or your job or making sure you take the trash out on Wednesday mornings. Yet, around all that you hope and dream between every necessary moment. For example, on the way to work you see a Porsche you'd love to have or a guy playing with his kid in a park. Two improbabilties really. One's monetary or more of a possessive need. You gotta save and earn money and maybe with some luck and work hard you'd get that Porsche. The other, is not monetary, but equally a challenge because you've got to meet the right person or be in the right situation or have some luck. In both cases, I feel fortunate and I see both situations more probable for my life yet, still improbabilites at this point. The other improbability in life I think is a challenge is instant success like winning the lottery or hitting that hole and one or getting a record deal. All of use strive for something like that or we wouldn't be creative or live in excess to achieve a goal like instant success. You can have all the right tools and for that matter, the right luck, yet still come up short in life. Funny, as I wrote the last sentence the song "Wishlist" by Pearl Jam came on my XM Radio. The fact remains, no matter who you are, just like the song playing now, you always wish for something more or to be someone your not.
In Sideways, Paul never gets what he really wants or is never perceived as how he wants to be. He's got his plan for a good week's vacation full of good eats, good wine and golf. Yet, nothing goes as planned no matter how well scripted he had it. He has to fend off a lie by his friend on his book publishing deal. He's insecure because of his past life experiences being married and then being rejected. He's uncomfortable with his friend's life of debauchery and deceit of his own fiance. He's also got to tell the truth no matter how much it's going to hurt. What a quagmire, yet a unique set of real life experiences most people face everyday. (Yes, I have hit a golf ball back at someone, twice!) So I guess what I am saying here is, we all have flaws and we all fear rejection, deceit and lies. Some more than others... Some of us can accept rejection, deceit and lies. But we can all have dreams, one and a million chances, even if they are only fun moments of imagination we can only just think of.