A deposit turns a possible plan into something that now has a cost to change.

Money changes the status of an intention. Before the deposit, the trip or the venue or the course is an idea that can be quietly dropped, and afterwards it has weight: cancelling now costs something, so the plan starts defending itself. That is useful when the plan is good, and it is also how people end up going through with things they had already stopped wanting.

Before you commit money, ask whether you want the plan or only the momentum. Afterwards, if it turns out to be wrong, treat the deposit as spent rather than as an argument. What you already paid should not decide the next few months.