2 of 3 cats use box just fine, why doesn't the third?

[G odishere4u2]

Hello, and thank you for your time!

2 of 2 cats use box just fine, why doesn't the third?

Well I just severely got crabbed out by the respondiers, though I deeply appreciate your answers. First of all, I will never punish a cat again, as now I know this will not help. Secondly, I forgot to mention originally that I already had the third cat checked out by the vets and no medical problems were found. Thirdly, I have already put an additional cat box in that guest bathroom. And last, I do feel bad for punishing the cat and I do extremely honor all of the advice that I have just received. Thanks!