A sudden thought had struck him.

他突然有了一个想法。

youdao

A sudden thought made her scramble to her feet.

她突然冒出一个的想法，急忙站了起来。

youdao

She was struck by the sudden thought that he might already have left.

她突然想到他可能已经离去。

《牛津词典》

The trouble with the Recency Effect is that everyone all of a sudden thought they were Nassim Taleb, orinthological experts on the spotting of Black Swans.

FORBES: Sometimes It's Just A Black Duck

And all of a sudden he started singing and I thought "wow!"

BBC: Obituary: The Troggs' Reg Presley

Also speaking on Newsnight Scotland, Harry Reid, former editor of the Herald newspaper, who is currently writing a book about Scotland's relationship with religion, said he thought the cardinal's "sudden departure" would "leave a gap" in the Catholic Church in Scotland.

BBC: Cardinal Keith O'Brien 'right' to resign ahead of conclave