Blake Treinen, the A’s new closer, had perhaps the best possible training for his high-stress job, one that requires the ability to remain unaffected by inevitable failures. Treinen, 29, never got a break as an amateur, overcoming obstacle after obstacle to make a Division 1 baseball team. The big leagues? A crazy notion. “If someone wanted to grab hold of it, it’s a Disney story in the making,” said former minor-leaguer Don Czyz, who helped Treinen finally find a college landing spot. As a youth, Treinen had juvenile rheumatoid arthritis, which causes joint inflammation and stiffness. Apart from playing Little League, he spent most of his time indoors and wasn’t in terrific shape, often going through a two-liter bottle of soda in a couple of days. “I wasn’t very active, didn’t have great eating habits, but what kid in junior high does?” Treinen said. “I was snacking on candy and soda and that led to weight gain and put me borderline prediabetic.” That diagnosis kicked him into gear: With exercise — he began running every night — and reduced sugar consumption, the weight came off, and the arthritis went away. Even so, Treinen was not remotely a prospect coming out of Osage City High School in Kansas, where he played baseball only his final two seasons and wasn’t a standout. Playing at Kansas State, his dream school, was out of the question, so Treinen went to Baker University, an NAIA school in Baldwin City, Kan., and pitched in three games on the junior varsity team.