just under the surface

[kjc0123]

What is the meaning of "just under the surface" in the following sentence?

As tough as he tried to act, Forrest's emotions were always just under the surface

[Ceh]

Forrest was trying to appear tough, though that's not what he was feeling, and he was close to expressing the way he really felt. Or something...

[Englishbird]

I would guess that it is a metaphor - if you imagine a lake and a fish that swims deep will not show any movement in the water on the surface, a fish that swims very close to the surface will distort the water on the surface, without necesarily being seen itself.

So as ceh says in the sentence, Forrest is trying to act tough, but it's fairly obvious that this is not how he feels, as his emotions are 'just under the surface' whereas if his emotions were hidden deeply then they would not be so obvious and he may appear as tough as he wants other people to see him.