According to the Stoics, there are three reasons to ‘thoughtfully contemplate the bad things that can happen’.
The first is to develop strategies to prevent those things from happening.
The second is to minimise the results of any bad things that do sneak through - Seneca said “he robs present ills of their power who has perceived their coming beforehand”.
But the third reason is the most important - to prevent us from taking for granted what we already have.
I would argue that rather than being three distinct reasons, they are actually three steps in a process - so if you find yourself worrying about what might happen, make sure you finish with love, joy and gratitude for everything that you already have…