put on a brave face

put on a brave face / front AND put on a bold face / front (to try to hide the fact that you are feeling upset or disappointed ) — держаться мужественно; не растеряться; не показывать вида (в трудных или опасных ситуациях); держаться так, как будто ничего (страшного, опасного и пр.) не происходит; не падать духом; ≈ держаться молодцом
Also put up a brave/good front (pretend to be happy, fool people about one's status)

Example 1: I had to put on a brave face and try to show him that I wasn't worried. (OALD)
Example 2: He was really upset over a poor grade but didn't want anyone to know. He smiled and put up a good front.

Example 3: You do the best you can — what you can, which mostly consists of putting on a brave face and not turning your eyes away from whatever horror's in front of you; although there may be opportunities for more direct action. (John Langan, "How the Day Runs Down", 2008)

Example 4: Despite all the painfully honest emotion, you can almost see Scott giving a sly wink as he sings. It sounds as if he's reflecting on a lifetime of frustrations and still putting on a brave face. To hear Scott sing it, you could almost believe there really is a magic place where skies are always blue and dreams do, eventually, come true. (Review: Jimmy Scott's new CD "Over the Rainbow")

put a brave face on sth — мужественно, стойко принять что-л.; не показывать вида, что что-л. расстраивает, огорчает, волнует, пр.;

Example 1: She put a brave face on her illness. — Она стойко, мужественно переносила свою болезнь. Болезнь не сломила ее. (OALD)

Example 2: From his hiding place around the corner of the building, Magnus watched as the boy Elio tried to put a brave face on things, and failed. He hugged himself tightly, his heart beating in fear, watching the other boy. (Mercedes Lackey, Rosemary Edghill, "Mad maudlin")

Example 3: Meanwhile, Sandy puts a brave face on being mother to a baby, who is evidently abnormal. (Ian Watson, "One of Her Paths ")

Example 4: Employees are putting a brave face on yesterday’s news. (MM)

Cf.:
[poker face]

Related vocabulary:
[grin and bear it]
[take the rough with the smooth]

[count your blessings]
[like it or lump it]