Lookup "occupancy chart antidepressant", study the chart. There is an exponential drop-off at lower doses. Hence to taper off without feeling it, one needs to cut smaller and smaller doses, (or liquify) which may be impractical.

Interesting; I wasn't aware that 20mg was considered the minimum effective dose for fluoxetine. I tried tapering from 20mg to 15mg (alternating 10/20) after ~4 years and was absolutely fine; I then tried the next step down to 10mg and crashed hard. Probably going to stay on it for life now, which is fine; I never really experienced any negative side effects.