The Short Answer: Yes if we’re talking about subjects and verbs.
The subject and verb of a sentence must agree with one another in number whether they are singular or plural. If the subject of the sentence is singular, its verb must also be singular; and if the subject is plural, the verb must also be plural.
Example 1:
Incorrect: An important part of my life have been the people who stood by me.
Correct: An important part of my life has been the people who stood by me.
Example 2:
Incorrect: The two best things about the party was the food and the music.
Correct: The two best things about the party were the food and the music.