Hey, Emily! I'm assuming you're talking about the problem I start at 6:07 (in red), and in fact, in that problem, I oxidize every -OH I can. To oxidize (whether you're using PCC or H2SO4/Na2Cr2O7), you need at least a C-H bond. Those C-H bonds are replaced with C-O bonds. Since this problem is using the Jones reagents, you can see I oxidized the primary alcohol (bottom right) to be a carboxylic acid, I oxidized the secondary alcohol to be a ketone, but the tertiary alcohol (which has NO C-H bond) remain unchanged since it couldn't be oxidized--there was no C-H bond to replace. Does that make sense? Please let me know if it does or doesn't (also thanks for watching!).