So, when you're stuck in a situation like this, unless people's lives are on the line, you say, "I'm telling you that we're risking <this problem>, but we will go with what you're saying." This is a win-win for you.
Either you're wrong, in which case the project is hopefully successful. You win because no one is going to remember your reservations if you are professional with them.
Or you're right, and you bring up your objections saying that you thought this would happen, and then you move one to correcting the situation.
Of course this won't always work if the repercussions of the failure are too large, like a business going under (or astronauts dying). But in less dire circumstances, just let them have their way. Either they learn you know what you're talking about, or they keep failing.