Imagine you have a friend named Jack who has a big jar of marbles. Every day, Jack takes out some marbles and counts them. You notice that after a while, Jack always gets the same number of marbles each day. This is called sure convergence.
Basically, sure convergence means that if you keep doing something over and over again, you will always get the same result. This can happen in lots of different situations, not just with counting marbles.
For example, say you have a recipe for making chocolate chip cookies. You follow the recipe exactly every time and always end up with delicious cookies. This is another example of sure convergence.
Overall, sure convergence just means that you can be sure of the outcome if you keep repeating the same process.