What the choice actually decides

A stream is not a personality test and it is not a verdict on ability. It is a decision about which entrance exams you will be eligible to sit in two years, and therefore which undergraduate courses will accept your application. That is the whole mechanism, and stating it plainly removes most of the drama.

The reason it feels enormous is that it is made at fifteen or sixteen, by someone who has never met an engineer, an accountant or a designer at work, on advice from adults whose own information is a decade or more out of date. The stakes are real. The information available at the moment of choosing is genuinely poor, and it is worth saying so rather than pretending otherwise.