We hear that the simplest things are often the most difficult to carve well because there is nothing to hide the flaws with. Its like singing karaoke without the echo, instrumental accompaniment and backup vocals -- the singer has to be damn good in order not to fall flat.
Some of the seemingly easy-to-carve bits are actually terribly difficult to carve.
Just a couple of examples:
1. The bugis pistol-grip handle. The form looks easy enough, but it has to feel right when gripped in the hand. Javanese/Madurese knock-offs of Bugis handles looked essentially the same, but is stiffer and doesn't feel right. This is because there should be an almost imperceptible twist in the 'head' of the handle. The other thing is -- notice the lines on the handle, especially the 'u-turn' double-line on the top back of the hilt (2nd pic). This is carved free-hand and on a curving surface, and the carver has only one stroke to do each line of that 'u-turn'. 1 mm off, and the lines don't join with the other lines properly.
2. The 'locust neck' sheath stem bottom. Looks plain and simple, but it is really quite difficult to shape from a square block. The inverted 'v' curves must fit perfectly between the 2 blocks of wood. 0.5mm off for any of the 4 curves on the inverted 'v' on either side and it won't fit.