Arabic writes twenty-eight consonants with fewer than twenty distinct shapes. The gap is closed by dots, and the group of jim, ha and kha is the clearest case in the alphabet. All three are the same stroke: a hook running down into a bowl that falls below the line and curls back. Ha carries no dot at all, jim carries one dot inside the bowl, and kha carries one dot above the hook. Nothing else separates them, and in unpointed writing they are one letter.
This is a consequence of how the script arrived. The Nabataean cursive from which Arabic descends had already collapsed several distinct Aramaic letters into single shapes, and Arabic then needed to write more consonants than Aramaic had, not fewer. Rather than invent new letterforms, scribes reused the shapes they had and marked the difference with points. The same solution produced the five letter ba group, the sin and shin pair, the sad and dad pair, the ta and za pair, and the ayn and ghayn pair. Roughly half the alphabet is a pointed variant of another letter.
The consequence for reading is that Arabic dots are not diacritics in the sense that an accent is. They are part of the letter. A missing dot is not an accent left off but a different word, and the earliest Quranic manuscripts, written without consistent pointing, could be read in more ways than a fully pointed copy allows. That is a matter of record rather than of controversy, and it is one of the reasons the science of the variant readings and the chains of oral transmission carried an authority the written page could not.