The person who notices your progress may be seeing what your daily view misses.

Change is invisible at close range. You live at the current level of whatever you are working on, so the improvement gets absorbed into normal and only the remaining gap stays visible. Someone who sees you every few months is comparing two snapshots instead of standing inside the film, which makes their view more accurate on this particular question, not merely kind. Their surprise is data you cannot generate yourself.

When somebody says you have come a long way, ask them what specifically looks different. Write the answer down for the next time you feel stuck in the same place.