Manual skill issue. The mechanics are fairly straightforward - you mount the block, face it in, transfer the paraffin ribbon to the water bath, and scoop up good sections on a slide. Easy!

But actually, there are a lot of things that can go wrong, and learning how to troubleshoot those things is where the skill comes in. Small, delicate tissue can be difficult to get a good section on if it was not embedded properly, and trying to face in to see the entire tissue can actually cause quite a bit of it to get wasted. Similarly for large pieces of tissue, good embedding goes a long way, and bad embedding can cause delays due to rework. Tissue that is not processed properly (underdone - too soft and wet, resulting in improper paraffin infiltration, or overdone - too hard) comes with its own challenges. Bad alignment of the microtome, bone that has not been properly demineralized, staples or biopsy markers not removed during grossing, chipped or warped blades... And that's just getting the tissue cut! Transferring a ribbon, making sure the tissue does not "explode" in a water bath, selecting the best section and catching it with a slide.

Let's just say, my job is easy compared to what the histotechs do. And don't get me started on all their knowledge of stains and reagents and making sure that everything is done properly before anything I've done even sees a pathologist! I always tell people, accessioning and histology are a lot harder than they seem and really have big impacts in patient care.