What is it that was tiring about the practice? Did they do it properly, or was the focus placed on tremendous output driving the feeling of a need for commensurate tremendous input on a daily basis? Most lifetime productive users only made a few cards a day, but I get the feeling that many who start, think they should be creating 20 cards a day and that is definitely a road to burn out. This feeling is compounded by digital tools that make it easier to quickly capture ideas by quoting or cut and pasting, but which don't really facilitate the ownership of ideas (internalization) by the note taker. The work of writing helps to facilitate this. Apparently the framing of literature note vs. permanent note also was a hurdle in the collection of ideas moving toward the filtering down and refining of one's ideas. These naming ideas seem to be a general hurdle for many people, particularly if they're working without particular goals in mind.

Only practicing zettelkasten for a month is certainly no way to build real insight or to truly begin developing anything useful. Even at two cards a day and a minimum of 500-1000 total cards to see some serendipity and creativity emerge, one would need to be practicing for just over a year to begin seeing interesting results.