Think you've mastered lap sau by the time you get to intermedate classes? You haven't.
When you start rolling with guys who have been training for many years you realise that your technique is loose.
I can see that my strikes are not always perfect centre and sometimes my bong is collapsing. This is especially true at speed. I hadn't noticed when rolling with beginners because their technique was equally loose. When you do it with experienced students, though, their consistency of shapes highlights the inconsistency of your own.
The same goes for chi sau and, by extension, everything else you do in wing chun.
Experienced students can replicate the same shape over and over again with amazing precision.
Roll with advanced students, especially those who have been training seriously for 10 years or more, and it's like trainng with a robot.
Ask these guys to throw a bong forward 100 times in a row and they will do it almost identically every time. How do they do that?
I think the answer is simple repetition. Do it over and over and over again and your muscle memory will be so strong that your body will be pre-programmed.
I had to take a week off from training recently so I decided to try to use any spare time I had to make myself more robotic. I knew my tan was weak so I practised the bong-tan move 50 times a day. When I went back to chi sau the next week, it had made a significant difference. It made me realise that practising the form is incredibly important.
Make your form robotic and all of your shapes will be consistent. I'm going to go and run through it a few times now...