For me it was hand and finger fatigue. Since I could not find a layout/design that I found ergonomic enough for my finger placement I have designed my own keyboard with these key ergonomic features:
- split keyboard design
- 58 keys, 4+1 thumb keys
- aggressive column stagger, fitting medium to large hands (3 design iterations needed to find the perfect layout)
- 18mm distance between rows instead of 19.05mm
- low keyboard height (single PCB/no casing, Kailh choc low profile switches and keycaps) to eliminate the need for wrist pad/raisers
- tactile switches, 57 grams
- QMK layers + tap dance etc
- Colemak-dh key mapping