Sometimes people are ready to go and solve big nasty problems or lead a team for the first time or design a custom memory manager for that C++ server application. Sometimes not. The trick for managers is to be reasonably sure that your chosen one will succeed. If you aren’t sure then put in a safety net or someone is likely to get hurt. Consider providing a mentor/coach for the task. Another idea is to meet regularly to track progress and to arrest the slide into failure or to mitigate the consequences.
Managers have a duty to ensure that their staff are not placed in a position where they are likely to fail or where failure will cause them to suffer. To do so unfairly risks reputations, happiness and health. I’ve seen too many decent, hard-working people damaged by careless and selfish task assignments. This is not to say that people should be mollycoddled. There is a middle ground.
Do you send people out to fight dragons before they are ready?