On the occasion of every event that befalls you, remember to turn to yourself and inquire what power you have for turning it to use.
In a way this is following on from part 8's advice on wishing (not merely accepting) things to be as they are, and also part 9's encouragement to not let unpleasant situations cloud our thinking. In many ways this is the pactical follow-up of those two more philosophical sections.
It is also, of course, an implementation of the dichotomy of control: when things happen to you (by definition, not in your control), ask yourself how you can use them for something that is in your control.
If you see a fair man or a fair woman, you will find that the power to resist is temperance. If labor be presented to you, you will find that it is endurance. If it be abusive words, you will find it to be patience. And if you have been thus formed to the proper habit, the appearances will not carry you along with them.
Some examples to get you on the right track. The last line is deceptively deep, and explains the point of the last 3 parts. By wishing things to be as they are, by staying vigilant during challenging times, and by turning every situation into a way to practice your Stoic reason, you are breaking the habit of just reacting. Or, as Viktor Frankl puts it:
Between stimulus and response there is a space. In that space is our power to choose our response. In our response lies our growth and our freedom.
Which I like to re-phrase as:
Grace exists between action and reaction