Just because you go down, doesn't mean the bidding was wrong. Especially at matchpoints, which is what this sounds like. OK, you got a few zeros going down in 3NT. But if you make a habit of playing in 4 or 5 of a minor instead, some of those will be zeros as well - for failing to be in 3NT when it makes. Probably more of them. Several things have to happen to go down in 3NT (when you otherwise have the goods to make it). First, you have to have a weak suit; second, they have to lead it; third, they have to not block the suit, or otherwise misplay it to give you an extra stopper. Opponents are not infallible! On top of that, sometimes you will have 9 cashing tricks after your one lonely stopper is driven out, say if the finesse you need works. On the whole, bidding 3NT with shaky stoppers pays off in the long run at matchpoints.