Looking up...
She felt incapable of solving the complex math problem.
She couldn't do the math problem because it was too difficult.
Not having the ability, skill, or capacity to do something
The child was incapable of understanding advanced physics.
The child was too young to grasp complex physics concepts.
He is incapable of lying to his parents.
He always tells the truth to his parents.
Often used to describe a lack of ability or skill in a particular area.
Use 'incapable' to describe a lack of ability in a general sense, not just physical limitations.
From Middle French 'incapable', from Latin 'incapabilis', from 'in-' (not) + 'capabilis' (able to hold, capable).
Often used to describe a permanent or inherent lack of ability, rather than a temporary inability.