Nisha says her single vote will not change the result either way, so there is no point going

Why

Nisha's arithmetic is honest and almost always correct — a single vote very rarely decides a seat, and pretending otherwise would be a lie. The trouble is that her reasoning does not belong to her alone. Every other voter can say the identical sentence with equal truth, and if they all act on it there is no election left. An argument that destroys itself the moment everyone follows it has something wrong inside it, even when each individual step looks sound. There is a second thing her arithmetic misses: parties study which groups turned out, and they spend the next five years courting those who did. Young voters who stay home are not just absent on one day, they are absent from the calculations. Test: look at which age groups vote heavily and whose concerns fill the manifestos. The flaw is that the reasoning generalises — 'my one action does not matter' fails exactly when everyone is entitled to say it.