It’s likely that both players are responsible.

North-South have reached a very poor contract. As so often, each of the two players considers that their partner is responsible for the accident. And you, what do you think?

Problem 1

The facts:

3NT and 4 Hearts are laydown, 5 Diamonds is also an excellent contract. One of the two players (or maybe both) has bid his hand badly.

Arguments

North: “Your Kings in my two suits are worth a fortune. I don’t agree with your 2NT bid, it’s well known that this is a conventional weak relay.”

South:  “To be honest, I couldn’t find a better bid. A fourth suit forcing 3♣ seemed to be an exaggeration, and it’s also inappropriate given that I stop that suit myself.”