Yes, but for many people who do not know how to do X, there is the chance that looking into the problem on one's own will result in a solution that can be accomplished in a reasonable amount of time. It's just unknown to that person at the start.

YET, if said person raises concerns immediately, there's also the potential for that work to get reassigned in a manner that never gives the said person to learn how to do X.

I agree that this is a selfish action, and ideally we do not act in such ways when under pressure to perform and work as a team. But I've found that this psychology often explains why teams find themselves with facing a Canary MacGuffin.