If you keep injecting in your favorite spots over and over without letting the veins repair themselves they will become leaky, making your shot less satisfying and harder to hit; could become seriously infected; and will eventually collapse or scar so badly that they become altogether unusable and interfere with circulation. So, it is very important to rotate the sites you use to inject. Try to use a new site for each new injection and go back to sites you’ve already used only after they’ve had time to rest and repair themselves.