A gratitude jar works on a simple mechanism: a small note is written each time something good happens or is noticed, then dropped into a jar, with the accumulated collection read back, often at the end of a year, as a concrete, physical record of accumulated good moments.
The physical object does real work here that a digital list often does not manage as effectively, since a jar visibly filling up over months offers a tangible, ongoing signal of accumulation that a phone notification or app entry, however well designed, tends to lack entirely.
Reading the notes back later, often months after they were written, tends to be more powerful than writing them in the first place, since many of the small moments recorded would otherwise have been completely forgotten by the time the jar is finally opened. It is a habit built more on repetition than inspiration, which turns out to be its real strength.