You learned it for one language. Now imagine that you're working with a handful of languages regularly, some of which have 1-based indexing, some 0-based, some of which may have closed ranges, others half-open ranges.
If you're anything like me, you'll end up spending quite a bit of time looking up the documentation to the range operator to remind yourself how this week's language works again.
Once I knew these two facts, it didn't add much confusion.
1. Indexing starts from 0
2. Thus, range can be thought "from up to one before x", x here would be 15.
And I learned this pretty early and did not get confused later on.