In math/geometry why do they always skip the letters I and J when labeling points or vectors?

How many letters in a row are you seeing in use in a diagram: something like ABCDEFGHKLM...? Please give some better context with actual examples where you see I and J being skipped.

Mostly i as an imaginary number, although a few other things play in. Lots of people write i and j very similarly as well. It's important to use letters that are easy to recognise and distinguish when you label things. Also, the three letters you mention are also very frequently used as indices in sums / series / products / components of vectors. You don't want to talk about the ith component of vector j.

Well, first, i is an imaginary number, so not very convenient. Also, i, j and k are the standard coordinate vectors in R3, so maybe to avoid this confusion too

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