The author of this sentence cannot be verified, and it may come from a sad sentence on the Internet.
Understand:
Yesterday has passed, there is no need to regret anything, just enjoy it occasionally in leisure.
Today needs to be grasped, because before you know it, he will become yesterday. The preciousness of today is that the quality you grasp determines your tomorrow. If you don't grasp today well, you will not only lose today, but also lose tomorrow.
In a word, seize today for tomorrow.