Strength is not just physical, but emotional, intellectual and spiritual.
No one is born strong. Strength comes over time through growth, development, watching, learning, practicing and straining. It is only through using and giving the strength you have that it can increase. You can not wait to be strong and then start using it. It starts from where you are and what you have. So learn, learn, learn, practice, practice, practice, train, train, train and you will see movement, strength and improvement.
Attempting something that is too big and heavy can bring on paralysis before even making a start. Starting small allows confidence and courage to grow as you gradually increase the pressure and strain. Like any muscle, when trained and practised, courage will become stronger and stronger.
Even the strongest and most capable need to rest. No one has an unlimited supply of strength and capability. Not enough rest means you will have fewer and fewer strong days. Like a muscle you need time to recover and rejuvenate, but weakness is temporary: no-one has to stay there.