Testosterone helps your mind to stay motivated and motivation is what drives us to accomplish things such as trying new experiences, reaching certain goals, and so on.
That is why depression is one of the earliest symptoms of low testosterone because the motivation you need to accomplish things is not there, which may lead to failure in accomplishing goals or not being satisfied when the goals are achieved.
In other words, when people achieve new goals in their personal or professional lives, they feel energetic, proud, and confident because they have optimal levels of testosterone. Besides, when they reach their goals, their bodies produce more testosterone to keep them motivated. It is a healthy cycle.
Therefore, if you want to feel motivated again and be able to reach and feel the accomplishment and pride, you need to elevate your testosterone and get it back to its normal levels.