A primary context for self control is time frame. A thing that may give pleasure right now will sometimes be less than optimal over the longer term. Examples abound.
- Eating too much.
- Consuming alchohol or other intoxicants to extreme.
- Continuing some pleasurable activity when one should be sleeping.
- Spending all the money on hand for amusing activities.
There are, of course, huge numbers of other examples. Each of them has the aspect of a short-term pleasure at the cost of a long-term problem.
Self control will be what you use to participate only to a reasonable degree in such activities.
You must eat, for example. And choosing something pleasant to eat will add to your enjoyment of life. Yet you must modify this desire by staying in limits, and choosing food that is actually healthy. No matter how much you like donuts, you can't eat only donuts.
Self control is what keeps you from becoming self destructive in such things. Your self control keeps you from trying to subsist on some type of food like donuts or pizza or whatever food tastes best to you. It guides you to think of your long-term health, not just what is pleasant right now.
This is a factor that is very nearly universal across all of humans. Our ancestors had times when resources were scarce. If food was available and not eaten, then it probably was either wasted or eaten by somebody else. Or some non-human organism ate it. So there was survival value in eating all food available. And it was rare that there was enough food to produce long-term health problems from eating too much. So humans have appetites that push us to consume anything available.
With modern technology it is relatively easy to procure enough food to satisfy your requirements. But your appetites are driven to keep consuming well past what is in fact good for you.
Similarly for many appetites other than for food. Intoxicants, sex, amusements of some kind, etc., will have a strong tendency to cause us to over indulge. It is our self control that allows us to stay in limits of healthy consumption.
An additional aspect of self control is emotional control. Interacting with other humans will frequently produce some degree of irritation. Even if it is innocent, such as when another person does something entirely by accident. They bump into you when they walk by. They drop something. They use the wrong word.
If you permit your emotions to hold sway, you may have violent outbursts at tiny provocations. Becoming violent because somebody picked up the wrong fork is going to produce troubled family dinners. And it will very likely result in you getting ostracized.
It is self control that allows the response to be held to a reasonable level in keeping with the size of the offense. And also in keeping with social norms for such situations. And so permits you to have relationships.