Serial position effect
The serial position effect is the way you remember the items at the start and the end of a list better than the ones in the middle. So if you study a long list of facts, the stuff in the middle tends to slip away first.
When you learn a list, two things help the ends stick. The first items get more of your attention and make it into long-term memory. The last items are still fresh in your head when you try to recall them. The middle gets neither, so it fades.
This matters for studying because your notes and chapters are basically long lists. The terms you meet in the middle of a session are the ones you are most likely to blank on later. They are not harder, they just sit in a weak spot.
The fix is simple. Notice which parts land in the middle and give them extra review. You can also break a long list into smaller chunks, so more items get to be a start or an end.
Mia studies 20 anatomy terms in one sitting. A day later she nails the first five and the last five, but keeps mixing up the ones in the middle. So she pulls those middle terms into their own short deck and reviews them on their own.