Word to describe "concealing" positive emotions, in fear of being perceived as irrational

This will be a bit hard to explain, but I'll give it a shot.

I am looking for a good word to describe: A person hiding his intense positive enthusiasm and excitement for something, as to not seem overly excited and hence being perceived as emotional or irrational. This person is afraid that his excitement might generate some sort of mistrust with the cautious person who will decide if he will be able to experience what he is exited about or not.

Example sentence:

"He is a true pragmatist; one who takes on new challenges with great, yet [word here] enthusiasm."

I have been thinking about using concealed, reserved, humbled, restrained and modest, but I feel like those words come with a sort of negative undertone, as if the person is harbouring some kind of hidden agenda, which is not what I want to say. Any suggestions?

Solution 1:

Words like seemly, proper, careful, knowing, canny, shrewd, astute, and decorous may fit. With slight rewording, phrases like with appropriate reserve, in reasoned measure, carefully proportioned, and not unseemly can be made to work. Of the above, canny ("careful, prudent, cautious" or "knowing, shrewd, astute") may serve best, because of its connotations of conscious, knowing insight and an eye to the main chance.

Solution 2:

How about "guarded"? It means "noncommittal", "restrained".

Solution 3:

The syntax you’ve committed yourself to makes it tricky. How about “with great, yet closeted, enthusiasm”. Or with “covert” for “closeted” (though I rather like “closeted” here).

With different syntax you could go for: “... yet does not display any (outward) sign of enthusiasm” or “suppresses any display/sign of enthusiasm”.

Slightly less transparently, you might play on the expression “to play one’s card close to one’s chest” (meaning, not to let on about what you are doing or have prepared): “he plays his enthusiasm close to his chest”.

Solution 4:

stoic: One who is seemingly indifferent to or unaffected by joy, grief, pleasure, or pain.

is the word that comes to mind for me.

Solution 5:

Perhaps the phrase tempered the expression of his enthusiasm might work.