We've all had an event in our lives when we've suffered a physical injury but delayed getting treatment for it. We might have been too busy with work, or maybe hoped it would heal on its own. Waiting can be risky however, as the presence of one injury could lead to others.
Let's say that you were playing basketball and twisted your ankle. Now you have a pain in your ankle every time you take a step. Such a pain is bound to change your gate, or how you walk, as your body automatically shifts your weight away from the troubled area. Now that you are walking with a limp you are putting your knee and hip joints at risk as they are being forced to carry your weight awkwardly.
Another example is a shoulder injury that leads you to minimize the use of the impacted arm, or stop using it entirely. This could lead to frozen shoulder, a serious restriction of your range of motion in the shoulder joint that can be quite painful to remedy, especially when you first start getting treatment for it.
Joint injuries tend to happen quickly but take a long time to heal. Although the primary goal is to always minimize the chances of them happening (via exercise and use of proper technique), a close second is to get them treated as soon as you realize something is wrong. That way one injury does not grow to several, impacting your ability to keep up with your fitness activities and leading to an overall decline of physical and emotional health.