1. Interface shock
Practising on PDFs or a different app means the real screen is new on the day that matters most: where the timer sits, how marking for review works, the on-screen calculator. Every second spent figuring out the software comes out of your answers. Rehearse on the actual exam interface until it is boring.
2. Untimed or loosely timed practice
Mocks taken with pauses, or "just finishing this one question", train a pace you won't have. Take full-length mocks in one sitting with the real time limits.
3. Fatigue in the last hour
Three-hour papers punish stamina. If your accuracy drops in the final third of mocks, that is a fatigue signal. Build up to full-length papers at the same time of day as your real slot.
4. Nerves and the first ten minutes
A hard opening question can rattle you for the rest of the section. Decide in advance what you'll do: skip anything that looks long, bank three easy questions first, then return.
5. A different question mix
Real papers can lean harder on topics your mocks under-weighted. Practise across many variants rather than one set, so no topic surprises you.
Close the gap
Treat your final mocks as dress rehearsals: same time of day, same interface, same breaks, no phone. The goal is for exam day to feel like your eleventh attempt, not your first.