At the time Lorca makes this statement, his motives are not entirely clear, except in as much as he wants it to be true. He also either does not understand, or does not fully believe, Lieutenant Stamets' previous assertions about the limitations on navigation. The fact that USS Glenn succeeded tells him that Discovery should be able to succeed, and he doesn't yet fully appreciate that nobody knows why Glenn succeeded, even though they do understand what caused Glenn's catastrophic end after it succeeded.
Since then, we have also learned that Lorca is actually operating under something of a cloud. Rather than going down with his ship, he lived to fight another day, but sacrificed his ship and crew to do so. We don't yet know the full context of this event (and as he says, context is for kings; without knowing that context, we can't fully appreciate his motives, yet). What we do know is that he's absolutely determined to prove it was the right decision by being the successful hero-captain Star Fleet needs to win the war. He's both driven and driving, and failure is simply not an option, in his mind.
So, it's possible he's simply lying, putting on the brave face and hoping to make it come true. It's possible that he honestly believes it when he says it because he's been listening selectively to Stamets. Either way, we, the audience, know that he actually got lucky, and that if he'd been wrong, no amount of blaming Stamets or even Burnham would have gotten him off the hook.