The Lebron James' quote says that our efforts may not be enough, and we may fail in some situations.
We need to be optimistic but realistic. We must always be rational, honest, and concrete.
We often do not have enough skill, ability, or intellect to succeed well in a situation, and we fail.
Indeed after failing, we will feel sad, but we must be aware that we could have done more. We should have been more skillful and handled the situation better. Also, by failing, we gain experience.
Once we are more experienced and good at that particular situation, maybe we get through it. If it doesn't happen, we repeat the process of integrating experience and consciousness until we overcome it. We should not be pessimistic and give up on something because we cannot solve it.