Grit, Character come from adversity. How you can let your child fail?
Is she able to do/handle/respond/deal with it? Is she willing?
The question of capability helps you determine if your child has the skills — social, cognitive or physical to do something. Is she capable of packing her own lunch? Is she capable of speaking in front of a crowd? Is she capable of reading to complete this homework? How do you know her capacities? Ask yourself what past experiences and skills has she demonstrated that tell you she is capable.
If your child is capable, then its time to ask if she is able. Ability indicates whether she can now execute in a specific situation using the skills she has. Sure, she can pack her lunch, she has the motor skills but is she able to? Is she able to perform given her mood, temperament, situation? Is there a way you can train her to do it? The question of ability is often tied to the child's emotional readiness to engage a piece of work. To discern what might be going on for your child emotionally, ask if she is motivated, sees the point, is driven and desires doing what you hope she will do.
By separating the capacity versus the ability to do something, parents can begin to let their children fail. If a child is capable, perhaps all you need to do is train her briefly by having a quick conversation, a comment that motivates her. Then, let her go at it and fail if needed.
Her failure will build her ability. And the rest will follow, as Tough says.