This phrase is grammatically correct and can be used in written English.
It is used to emphasize that someone is giving a lot of thought and consideration to a certain topic or situation. Example: "Before making a decision, I urge you to think very seriously about the potential consequences of your actions."
"I'd have to think very seriously about that," Hodgson said.
"To start assassinating American citizens without charges – we should think very seriously about this".
So I began to think very seriously about colour, light and composition.
All countries must think very seriously about adaptation and plan ahead.
"I would tell her she needed to think very seriously about whether that was a place she wanted to work..
"I think people need to think very seriously about what drives the decisions they are making," he said.
I worked part-time; I was lucky enough to be able to take extra time off; I thought, very seriously, about quitting.
I have thought very seriously about whether this is a place I want to work and whatever its failings, I really think this is where God has put me".
The last time people thought very seriously about shipworms — people other than shipworm scientists, that is — was likely in the late nineteenth and early twentieth centuries, when wooden ships still reigned.
"Some lawyers made the case that there might be avenues to pursue," Mr. Daley said, noting that one in particular, whom he would not name, "thought very seriously there was a long shot" of returning to the Florida Supreme Court.
"Sir, it is now that I have thought very seriously about the families," Duckenfield said, explaining that the video was the most moving thing he had ever seen, and that it had shown him "what it means to a mother to lose a loved one".
