Compulsory voting doesn’t mean you have to vote: it means you have to show up or have a good excuse to not have done so. Once you show up, you can lodge a blank ballot, write “FUCK THEM ALL” on the paper, draw a willy on it or whatever. Informal votes, as they’re known, are counted and, while they don’t decide who wins, they’re a gauge of dissatisfaction (a certain baseline amount is expected, though variation from that can indicate changes in public sentiment).

From an individual voter’s point of view it may seem pointless and annoying, though looking at it across the system, compulsory voting changed the dynamics of elections by eliminating the advantage of playing to one’s base to boost turnout. The result, as seen in jurisdictions such as Australia, is less extremism as parties tend to aim to appeal more to the broad public.