Willpower is the strength of your mind and your determination. It is what allows you to resist temptation or to do something that is difficult.
To expend is to use up, to use up all of something. When you expend energy, you are using up your resources, and you will eventually run out of energy.
The undergrowth is the part of the forest that is below the surface of the ground. It's usually full of plants and trees that have been hidden by the leaves and branches above.
To strategize is to come up with a plan to win a battle, to take control of a situation, or to achieve your goals.
An impulsive person is usually very quick to react, and they don't usually think things through very carefully. They often make decisions based on instinct rather than logic.
To squat is to sit down on the ground and put your feet flat on the ground. Squats are a very important part of a bodybuilding routine, because they help you to build muscle and strength.
To be knowledgeable is to have a lot of knowledge about something. When you are knowledgeable about a subject, you are able to understand it well.
Journaling is the act of writing down your thoughts and feelings in a journal. You can journal about anything that is on your mind, whether it's your thoughts on your day job or your thoughts on your personal life.