There are many reasons in the Psalms for why you should have long-term optimism.
First of all, in Psalm 72:17a it says ‘His name shall endure forever, His name shall continue as long as the sun’ so with that in mind it would probably be best to follow Him since He, the Lord, will always exist. Then in Psalm 72:17b it says ‘and men shall be blessed in Him…’ everyone wants to receive blessings right? Again in Psalm 37:9 it’s stated that ‘those who wait on the Lord, they shall inherit the earth.’
Secondly, it is spoken in Psalm 18:30 & 32 that ‘As for God His way is perfect… He is a shield to all who trust in Him… It is God who arms me with strength and makes my way perfect.’ Another great verse in the Psalms for a reason to have long-term optimism is Psalm 55:22 ‘Cast your burdens on the Lord and He shall sustain you.’
With all these comforting verses to show that God loves us why wouldn’t we have optimism in our lives to trust our Lord and His plan for us?