How do "they" create a flu vaccine in advance of its showing up when it is always morphing into something else? Do they try to outguess it?

Why does a virus change it's nature? A cat doesn't morph into an elephant. Born it a cat it remains a cat its entire life. Why are viruses/bacteria different? I expect they change to adapt so they can survive.

Would you like to be able to do that? Adapt/change so you can survive? Do you?