When someone senior proposes something flawed, "I disagree, that won't work" forces them to defend it. Now it's their ego vs. your point, and their ego wins. Instead, ask the question that leads them to the flaw: "How are we thinking about this handling the Q4 volume spike?"
If the flaw is real, they'll hit it themselves and an idea someone talks themselves out of dies, with no loser in the room. If there's actually a good answer, you just look thorough instead of wrong.
