If a player opts to create his/her own character, though, and pays attention only to endurance and intelligence, will there ever be a point where he/she simply can’t advance?
One of the great strengths of Fallout was the way two people could play different characters and have completely different experiences of the game. We've aspired to the same lofty goal with Lionheart: a character that specializes in brute force or a character that specializes in wizardry, sneaking, or diplomacy all have viable paths through the game. The classless nature of the SPECIAL system also allows a large number of hybrid characters. Some areas or encounters may be harder for certain characters than others, but I think you would have to try really hard to make a character that would run into a brick wall.