A lot of times, people talk about the need to get stronger. Especially athletes, or people who know they are weak. This leads them to hit the gym and the weights, in hopes of fixing their weakness problem.
But there is more than one type of strength. The ability to exert force is our most common expression of strength, but it is not the end all be all that some like to think.
The first is obviously that of physical strength. What everyone sees and acknowledges as the ability to produce physical force that is both concrete and visual. We can see the bar bending, or the number of reps. We can see the size of the person, and how much weight they can move. This is physical strength, and while it is good, it isn't always the answer to self-improvement.
The second is mental strength, which some often refer to as mental toughness. Mental strength is more skillful, and represents the ability to produce the mental force to push through physical and psychological hardship. It is the driving force behind physical strength. And while physically strong people often have high levels of mental strength, the two are not always intertwined.
The third and final form of strength is spiritual. While some may interrupt spiritual as religious, I find it can be expounded beyond that. Spiritual strength can also be found as strength of spirit. The ability to rise above emotionally challenging times and find joy or peace. In Viktor Frankl's book "Man's Search For Meaning", you'll find great examples of this. People who are strong in spirit have an uncanny ability to face the odds with joy and purpose.
It is not that either of these strengths is better than the other. It is that each compliments the other in it's own unique way. The strongest people are not ones who are just physically strong or mentally strong or spiritually strong.
They are those who blend components of each into one.