Always assuming the best isn’t the greatest option in every situation. If you assume the best about everything then you will be disappointed many times in life.
Then, on the other hand, you have people who always fear the worst. They see Murphy’s Law being applied everywhere; if something bad is possible, it will most likely happen. Like the last card you look at in your wallet is the one you needed. Or the last box you unpacked contained your toothbrush. These people are paranoid that the worst will always happen.
And, on the last hand (because we obviously have three), we have what I believe. I assume the best or worst to the point where I’m always grateful at the outcome. I may assume the worst at times but I don’t fear the worst. Assuming the worst leaves you without stress whereas fearing the worst puts unneeded stress on you constantly.
So, I would suggest you assume the worst, but don’t fear it, because if it turns out for the best, then you are in for a happy surprise!