It means: Only the beautiful years can't be disappointed, and the beautiful youth can't be wasted in vain. We should do more meaningful things in the short years, cherish sincerity and be kind to people and things around us.
This sentence is a sentence in the campus reading week held by Xi' an High School. The whole sentence is: April is the most beautiful day on earth, only time can't be wasted, only reading can't live up to it. On the road of fighting the epidemic, on the road of life, we are not alone with books!