To be optimistic implies to be hopeful in hard circumstances. In 1 Kings 4:1-34, the Shunammite woman whose only son died in her house was confident so much so that even when she got to Prophet Elisha, she still said It is well.
The Almighty God expects all His children to be optimistic. Just like I always say to people that my tomorrow shall be alright. I know for sure that this is true, yet, I will keep saying it till I see the Lord Jesus in glory. It doesn't matter what situation you are in, never give up.
Know that your future is bright; your wonderful hopes and dreams will come to fulfillment so long as you stay with the Lord Jesus. Never give room for worry because when you worry over small things, you will miss out on the huge things the Lord is preparing for you.
Matthew 6:25-26 encourages us not to be anxious about tomorrow because the Almighty God that feeds the birds knows our needs. So, when worry tries to come in, praise the Lord instead.