1. Size standards are not uniform: shoe size standards of different brands and manufacturers may be different. For some manufacturers, their size 40 shoes may be relatively small, so they need to use larger insoles to adapt to different foot types.
2. Individual differences: People's foot type and sole thickness are different, and some people's soles are thicker, so it may be uncomfortable to wear shoes of size 40. Using the insole with the size of 4 1 can provide additional foot support and reduce the pressure on the soles of feet.
3. Correct the inappropriate shoe size: Sometimes, people may choose a size that is not completely suitable for them when buying shoes. When they realize that the size of shoes is not suitable enough, using insoles can adjust the size of shoes to a certain extent, providing a better wearing experience.
It should be noted that the above are just some possible reasons, and the specific situation may vary from person to person. The best way is to try on shoes of various sizes and choose the size and insole that suits you best.