“Don’t get your hopes up”

[Odessa Dawn]

"Some people don’t set goals or New Year’s resolutions because they’re afraid to hope. Well-meaning families and friends tell them, “Don’t get your hopes up,” for that new job, new relationship, or new level of fitness. “You’ll only be disappointed.”
More: Hope for the New Year | Psychology Today

1.get something up: prepare or organize a project or piece of work
2. get up # 9. informal to be involved in

I couldn't catch the exact meaning of the underlined phrasal verb since I don’t know if there is a subtle difference between the above-mentioned definitions. However, I think that the main idea of that line is this "Blessed is he who expects nothing, for he shall never be disappointed."

Thank you,

[probus]

Yes, we sometimes tell a person "Don't get your hopes up" when we think his hopes are unlikely to be fulfilled.

[English4everyone]

Can it be a synonym for "don't raise your hope"?

[probus]

Synonyms refer to words, not sentences.

Your sentence means approximately the same thing as Odessa Dawn's, but is unidiomatic. In other words a fluent English speaker would be extremely unlikely to utter it. The sentence supplied by Odessa Dawn in the title of this thread is what one would expect to hear.