in programming, and in mathematics, it's always been weird to me that frequently paired variables are basically the most easily confused for one another pairs, especially when written quickly or sloppily.
u and v were so difficult for me to differentiate in handwriting. My handwriting is not that pretty and the difference between a round bottom and a sharp bottom is not that big when stressed in an exam.
When travelling in places where Latin script is not official (e.g. Middle East, Asia), I notice many mix-ups of pq and b. I always wondered how this would impact their ability to learn to program.