For my money, a knee-jerk reaction of "we can't do that" is something to avoid.
I've worked with many brilliant devs. Once they get a certain level of knowledge and experience, often there's a knee-jerk to a client or stakeholder request that it's not easily possible in whatever platform or code base we're working in. I'd say 75%-90% of the time after that, they usually come back on their own and say "oh, we could do it one of these ways with these trade-offs." But that initial knee-jerk can be disheartening.
I'd like to see more devs say "I'm not sure" before saying "no." A lot of seniors think saying "I don't know" is a bad thing. It's only bad if it's not followed by "But I'll find out!"
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