WARNING: The following contains SPOILERS for Young Sheldon season 5, episode 3, "Potential Energy and Hooch on a Park Bench."
The prequel series Young Sheldon just explained why adult Sheldon (Jim Parsons) decided to work at The Cheesecake Factory in The Big Bang Theory. Knowing full well of his intellectual prowess, the socially inept genius takes massive pride in his work at CalTech. So, it was such a surprise when he suddenly popped in at The Cheesecake Factory and worked there alongside Penny (Kaley Cuoco) and Bernie (Melissa Rauch) back in The Big Bang Theory season 3. Years after that, the CBS spin-off offers additional context for adult Sheldon’s bizarre decision.
The first couple of episodes of Young Sheldon season 5 focused on the budding romance between George Cooper (Lance Barber) and Brenda Sparks (Melissa Peterman). In fact, the show's titular character has been mostly sidelined since the season 4 finale, which revolved around Missy's (Raegan Revord) boy problems and the subsequent fight between his parents. Young Sheldon season 5, episode 3, titled "Potential Energy and Hooch on a Park Bench," continued this trend by primarily tackling Georgie's (Montana Jordan) decision to drop out of school. But, subtly, the outing actually revealed the reason why adult Sheldon suddenly started working at The Cheesecake Factory despite still having his dream job at CalTech.
In The Big Bang Theory season 3, episode 14, titled "The Einstein Approximation," Sheldon was stuck trying to answer a physics query. The problem kept him awake for days as he frustratingly tried to crack it. Stuck with no leads, he started applying for several menial jobs and ended up clearing and waiting tables at The Cheesecake Factory. It seemed like an odd way to cope with his predicament, but as seen in Young Sheldon, this might be something that he learned from Dr. Sturgis (Wallace Shawn), who, after getting fired at the supercollider, decided to work at a local supermarket store.
In Young Sheldon, the titular genius can't understand why his mentor, Dr. Sturgis, would choose to bag groceries rather than practice as a physicist. However, Dr. Sturgis is adamant that he enjoys his new job — he even finds joy in the simplest things. Remembering this in The Big Bang Theory, adult Sheldon may have thought he'd find some sense of fulfillment by being a waiter the same way Dr. Sturgis did while working in retail. Him seeing Dr. Sturgis' happiness firsthand likely inspired him to take a similar route when Sheldon faced his problem in The Big Bang Theory. Although he wasn't working at a grocery store, Sheldon pursued a similarly simple job at The Cheesecake Factory that could provide him with the same instant satisfaction that Dr. Sturgis felt as a supermarket staff.
It's unclear what lies ahead for Dr. Sturgis at this point in Young Sheldon, but it's not outside the realm of possibility that he eventually comes back to East Texas Tech as a teacher. Perhaps while working in the grocery, he comes up with a new great idea that persuades him to reclaim his old job. The lack of motivation on Dr. Sturgis’ part stems from losing his dream job; because of that, he's convinced that nothing else in the scientific field interests him anymore. However, just as waiting tables helped Sheldon, working at a grocery store may give Sturgis the creative spark he needs. Young Sheldon is often criticized for contradicting the events of its parent series, but this is actually a prime example of how it can subtly build on what's established in The Big Bang Theory while also carving its own story. That way, the spin-off can offer something fresh and interesting without turning off fans of its parent series who have been unimpressed with it thus far.